Bacteria1 Bacteria This article is about the microorganisms. For the genus, see Bacterium (genus). For other uses, see Bacteria (disambiguation). Bacteria Temporal range: Archean or earlier – Recent Scanning electron micrograph of Escherichia coli bacilli Scientific classification Domain: Bacteria Phyla Gram positive / no outer membrane Actinobacteria (high-G+C) Firmicutes (low-G+C) Tenericutes (no wall) • Gram negative / outer membrane present Aquificae Deinococcus-Thermus Fibrobacteres–Chlorobi/Bacteroidetes (FCB group) Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes–Verrucomicrobia/Chlamydiae (PVC group) Proteobacteria Spirochaetes Synergistetes • Unknown / ungrouped Acidobacteria Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Dictyoglomi Thermodesulfobacteria Thermotogae • Bacteria ( i/bækˈtɪəriə/; singular: bacterium) constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. They are also known to have flourished in manned spacecraft.[1] Bacteria There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals.[2] Bacteria are vital in recycling nutrients, with many of the stages in nutrient cycles dependent on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. In the biological communities surrounding hydrothermal vents and cold seeps, bacteria provide the nutrients needed to sustain life by converting dissolved compounds such as hydrogen sulphide and methane to energy. On 17 March 2013, researchers reported data that suggested bacterial life forms thrive in the Mariana Trench, the deepest spot on the Earth. Other researchers reported related studies that microbes thrive inside rocks up to 1900 feet below the sea floor under 8500 feet of ocean off the coast of the northwestern United States. According to one of the researchers,"You can find microbes everywhere — they're extremely adaptable to conditions, and survive wherever they are." Most bacteria have not been characterized, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology. There are approximately ten times as many bacterial cells in the human flora as there are human cells in the body, with the largest number of the human flora being in the gut flora, and a large number on the skin. The vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, and some are beneficial. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, and bubonic plague. The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and are also used in farming, making antibiotic resistance a growing problem. In industry, bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, and the recovery of gold, palladium, copper and other metals in the mining sector, as well as in biotechnology, and the manufacture of antibiotics and other chemicals. Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea. Etymology The word bacteria is the plural of the New Latin bacterium, which is the latinisation of the Greek βακτήριον (bakterion), the diminutive of βακτηρία (bakteria), meaning "staff, cane", because the first ones to be discovered were rod-shaped.[3] Origin and early evolution Further information: Timeline of evolution and Evolutionary history of life The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, all organisms were microscopic, and bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. This involved the engulfment by proto-eukaryotic cells of alpha-proteobacterial symbionts to form either mitochondria or hydrogenosomes, which are 2 Among the smallest bacteria are members of the genus Mycoplasma.0 micrometres in length. Later on. This is known as secondary endosymbiosis. others can be spiral-shaped. attach to surfaces. grain. but these ultramicrobacteria are not well-studied. as small as the largest viruses. or rod-shaped. called spirochaetes.5–5. Bacterial cells are about one-tenth the size of eukaryotic cells and are typically 0. Most bacterial species are either Bacteria display many cell morphologies and arrangements spherical. Some bacteria may be even smaller. Elongation is associated with swimming. swim through liquids and escape predators. fishelsoni reaches 0. E. called vibrio. More recently. called bacilli (sing. This wide variety of shapes is determined by the bacterial cell wall and cytoskeleton. in ancient "amitochondrial" protozoa). stick).Bacteria still found in all known Eukarya (sometimes in highly reduced form. which measure only 0. called morphologies. Morphology Further information: Bacterial cellular morphologies Bacteria display a wide diversity of shapes and sizes. called cocci (sing. e. eukaryotes engulfed a eukaryotic algae that developed into a "second-generation" plastid. or tightly coiled. coccus. Here. This led to the formation of chloroplasts in algae and plants. and is important because it can influence the ability of bacteria to acquire nutrients. called spirilla. 3 . The large surface area to volume ratio of this morphology may give these bacteria an advantage in nutrient-poor environments. A small number of species even have tetrahedral or cuboidal shapes. There are also some algae that originated from even later endosymbiotic events.[4] Some bacteria.7 mm. seed). However. bacteria were discovered deep under Earth's crust that grow as branching filamentous types with a star-shaped cross-section. a few species — for example.3 micrometres. Thiomargarita namibiensis and Epulopiscium fishelsoni — are up to half a millimetre long and are visible to the unaided eye. bacillus.g. are shaped like slightly curved rods or comma-shaped. from Latin baculus. some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms. from Greek kókkos. similar in appearance to fungal mycelia. when starved of amino acids. In these fruiting bodies. Bacteria living in biofilms display a complex arrangement of cells and extracellular components. Oregon. about one in 10 cells migrate to the top of these fruiting bodies and differentiate into a specialised dormant state called myxospores. and bacteria protected within biofilms are much harder to kill than individual isolated bacteria. protists and archaea. this type of cooperation is a simple type of multicellular organisation. Filamentous bacteria are often surrounded by a sheath that contains many individual cells. relative are often present during chronic bacterial infections or in infections of to those of other organisms and biomolecules implanted medical devices. the majority of bacteria are bound to surfaces in biofilms. and may contain multiple species of bacteria. Myxobacteria detect surrounding cells in a process known as quorum sensing. . approximately 20 mm thick. migrate toward each other. others associate in characteristic patterns: Neisseria form diploids (pairs). Certain types. For example. Even more complex morphological changes are sometimes possible. such as soil or the surfaces of plants. forming secondary structures such as microcolonies. Streptococcus form chains. which are more resistant to drying and other adverse environmental conditions than are ordinary cells. and Staphylococcus group together in "bunch of grapes" clusters. In natural environments. and aggregate to form fruiting bodies up to 500 micrometres long and containing approximately 100. Biofilms are also important in medicine. the bacteria perform separate tasks. Bacteria can also be elongated to form filaments. for example the Actinobacteria. through which there are networks of channels to enable better diffusion of nutrients. A biofilm of thermophilic bacteria in the outflow of Mickey Hot Springs. These films can range from a few micrometers in thickness to up to half a meter in depth.Bacteria 4 Many bacterial species exist simply as single cells. as these structures The range of sizes shown by prokaryotes. Bacteria often attach to surfaces and form dense aggregations called biofilms or bacterial mats.000 bacterial cells. For example. such as species of the genus Nocardia. even form complex. branched filaments. often grouped in chains called polyribosomes. such as energy generation. bacteria do not usually have membrane-bound organelles in their cytoplasm. in many photosynthetic bacteria the plasma membrane is highly folded and fills most of the cell with layers of light-gathering membrane. They lack a true nucleus. and their genetic material is typically a single circular chromosome located in the cytoplasm in an irregularly shaped body called the nucleoid. microscope image of carboxysomes in Halothiobacillus neapolitanus. but structures such as the prokaryotic cytoskeleton and the localization of proteins to specific locations within the cytoplasm that give bacteria some complexity have been discovered. proteins and other essential components of the cytoplasm within the cell. or expel undesired molecules from the cytoplasm. The nucleoid contains the chromosome with its associated proteins and RNA. The general lack of internal membranes in bacteria means reactions such as electron transport occur across the cell membrane between the cytoplasm and the periplasmic space. These "polyhedral organelles" localize and compartmentalize bacterial metabolism. use concentration gradients across membranes. below is an image because they have a double membrane of purified carboxysomes. around their nucleoids and contain other membrane-bound cellular structures. they are compartments within bacteria that are surrounded by polyhedral protein shells. Some antibiotics bind specifically to 70S ribosomes and inhibit bacterial protein synthesis. However. Like all living organisms. rather than by lipid membranes. Top left is an electron internal membranes in bacteria. Other proteins import nutrients across the cell membrane. Structure and contents of a typical Gram positive bacterial cell (seen by the fact that only one cell membrane is present). bacteria contain ribosomes. a function performed by the membrane-bound organelles in eukaryotes. . but the structure of the bacterial ribosome is different from that of eukaryotes and Archaea. These subcellular levels of organization have been called "bacterial hyperstructures". Many important biochemical reactions. and thus contain few large intracellular structures. These light-gathering complexes may even form lipid-enclosed structures called chlorosomes in green sulfur bacteria. for the production of proteins. As they are prokaryotes. Most bacteria do not have a membrane-bound nucleus. The phylum Planctomycetes are an exception to the general absence of Carboxysomes are protein-enclosed bacterial organelles. Scale bars are 100 nm. Bacteria were once seen as simple bags of cytoplasm. chloroplasts and the other organelles present in eukaryotic cells. This membrane encloses the contents of the cell and acts as a barrier to hold nutrients. mitochondria.Bacteria 5 Cellular structure Further information: Bacterial cell structure Intracellular structures The bacterial cell is surrounded by a lipid membrane (also known as a cell membrane or plasma membrane). Bacterial ribosomes have a sedimentation rate of 70S (measured in Svedberg units): their subunits have rates of 30S and 50S. On the right is a model of their structure. Micro-compartments such as carboxysomes provide a further level of organization. a cell wall is present on the outside of the cytoplasmic membrane. for instance. are membrane-bound vesicles present in some species of Cyanobacteria. Intracellular membranes called chromatophores are also found in membranes of phototrophic bacteria. Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. is responsible for the staining pattern of poor absorption followed by 6 . Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids. Most bacteria have the Gram-negative cell wall. These two groups were previously known as the low G+C and high G+C Gram-positive bacteria. sulfur or polyhydroxyalkanoates. Acid-fast bacteria such as Mycobacteria are resistant to decolorization by acids during staining procedures. such as Haemophilus influenzae or Pseudomonas aeruginosa. they contain bacteriochlorophyll pigments and carotenoids. which are freely permeable to gas. such as glycogen. Gas vacuoles. Inclusions are considered to be nonliving components of the cell that do not possess metabolic activity and are not bounded by membranes. Microcompartments are widespread. Certain bacterial species. They allow the bacteria to control their buoyancy. which is made from polysaccharide chains cross-linked by peptides containing D-amino acids. lipid droplets. which are made of cellulose and chitin. An early idea was that bacteria might contain membrane folds termed mesosomes. whereas if it is partially removed. Some bacteria produce intracellular nutrient storage granules for later use. and only the Firmicutes and Actinobacteria have the alternative Gram-positive arrangement. polyphosphate. it is called a spheroplast. The cell wall of bacteria is also distinct from that of Archaea. The cell wall is essential to the survival of many bacteria. In contrast. ß-Lactam antibiotics such as penicillin inhibit the formation of peptidoglycan cross-links in the bacterial cell wall. but these were later shown to be artifacts produced by the chemicals used to prepare the cells for electron microscopy. are composed of polysaccharides and lipid A that is responsible for much of the toxicity of Gram-negative bacteria. Used primarily for photosynthesis. produce internal gas vesicles. The most common inclusions are glycogen. and pigments. that contain magnetic crystals. Volutin granules are cytoplasmic inclusions of complexed inorganic polyphosphate. Lipopolysaccharides. a thick one in the Gram-positives and a thinner one in the Gram-negatives. found in human tears. such as the photosynthetic Cyanobacteria. A common bacterial cell wall material is peptidoglycan (called "murein" in older sources). which do not contain peptidoglycan. respectively. Magnetosomes are bacterial microcompartments. present in magnetotactic bacteria. also called endotoxins. These differences in structure can produce differences in antibiotic susceptibility. The high mycolic acid content of Mycobacteria. it is called a protoplast.Bacteria Those antibiotics kill bacteria without affecting the larger 80S ribosomes of eukaryotic cells and without harming the host. These granules are called metachromatic granules due to their displaying the metachromatic effect. Extracellular structures Further information: Cell envelope In most bacteria. crystals. If the bacterial cell wall is entirely removed. which they use to regulate their buoyancy – allowing them to move up or down into water layers with different light intensities and nutrient levels. There are broadly speaking two different types of cell wall in bacteria. The enzyme lysozyme. The plasma membrane and cell wall comprise the cell envelope. membrane-bound organelles that are made of a protein shell that surrounds and encloses various enzymes. The names originate from the reaction of cells to the Gram stain. and the antibiotic penicillin is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan. respectively. vancomycin can kill only Gram-positive bacteria and is ineffective against Gram-negative pathogens. they appear red or blue when stained with the blue dyes methylene blue or toluidine blue. Carboxysomes are bacterial microcompartments that contain enzymes involved in carbon fixation. a test long-employed for the classification of bacterial species. also digests the cell wall of bacteria and is the body's main defense against eye infections. Bacterial cell walls are different from the cell walls of plants and fungi. These structures can protect cells from engulfment by eukaryotic cells such as macrophages (part of the human immune system). Flagella are rigid protein structures. and vary in structural complexity: ranging from a disorganised slime layer of extra-cellular polymer to a highly structured capsule. and desiccation. such as high levels of UV light. It is implicated as responsible for the heat resistance of the endospore. Sporohalobacter. and Heliobacterium. The assembly of these extracellular structures is dependent on bacterial secretion systems. disinfectants. about 20 nanometres in diameter and up to 20 micrometres in length. They can also act as antigens and be involved in cell recognition. so are intensively studied. They are distributed over the surface of the cell. Fimbriae are believed to be involved in attachment to solid surfaces or showing multiple flagella on the cell surface to other cells. Flagella are driven by the energy released by the transfer of ions down an electrochemical gradient across the cell membrane. but are known to act as virulence factors in Campylobacter and contain surface enzymes in Bacillus stearothermophilus. in which the acid-fast bacilli are stained bright-red and stand out clearly against a blue background.Bacteria 7 high retention. Fimbriae (sometimes called "attachment pili") are fine filaments of protein. The most common staining technique used to identify acid-fast bacteria is the Ziehl-Neelsen stain or acid-fast stain. slightly larger than fimbriae. an S-layer of rigidly arrayed protein molecules covers the outside of the cell. Pili (sing. usually 2–10 nanometres in diameter and up to several micrometers in length. such as Bacillus. as well as aiding attachment to surfaces and the formation of biofilms. and are essential for the virulence of some bacterial pathogens. S-layers have diverse but mostly poorly understood functions. can form highly resistant. In almost all cases. In this . pressure. L-form bacteria are strains of bacteria that lack cell walls. Clostridium. heat. and resemble fine hairs when seen under the electron microscope. Endospores have a central core of cytoplasm containing DNA and ribosomes surrounded by a cortex layer and protected by an impermeable and rigid coat. Anaerobacter. They can also generate movement where they are called type IV pili (see movement. Bacillus anthracis (stained purple) growing in cerebrospinal fluid Endospores show no detectable metabolism and can survive extreme physical and chemical stresses. Many types of secretion systems are known and these structures are often essential for the virulence of pathogens. although Anaerobacter can make up to seven endospores in a single cell. Dipicolinic acid is a chemical compound that composes 5% to 15% of the dry weight of bacterial spores. Endospores Further information: Endospores Certain genera of Gram-positive bacteria. that are used for motility. These transfer proteins from the cytoplasm into the periplasm or into the environment around the cell. detergents. The main pathogenic bacteria in this class is Mycoplasma (not to be confused with Mycobacteria). below). below). Helicobacter pylori electron micrograph. one endospore is formed and this is not a reproductive process. pilus) are cellular appendages. This layer provides chemical and physical protection for the cell surface and can act as a macromolecular diffusion barrier. In many bacteria. freezing. gamma radiation. that can transfer genetic material between bacterial cells in a process called conjugation where they are called conjugation pili or "sex pili" (see bacterial genetics. Glycocalyx are produced by many bacteria to surround their cells. dormant structures called endospores. Bacteria are further divided into lithotrophs that use inorganic electron donors and organotrophs that use organic compounds as electron donors. but also many chemolithotrophic species. and the electron donors used for growth. the source of carbon. sulfate or carbon dioxide are used as electron acceptors. and endospores even allow bacteria to survive exposure to the vacuum and radiation in space. or based on chemotrophy. Steinn Sigurdsson. Hydrogenophilaceae. and acetogenesis. where organic carbon compounds are used as carbon sources. Chloroflexi. these organisms may remain viable for millions of years. and contamination of deep puncture wounds with Clostridium tetani endospores causes tetanus. meaning that cellular carbon is obtained by fixing carbon dioxide. Respiratory organisms use chemical compounds as a source of energy by taking electrons from the reduced substrate and transferring them to a terminal electron acceptor in a redox reaction. Energy metabolism of bacteria is either based on phototrophy. Green sulfur bacteria. whereas phototrophic organisms use them only for biosynthetic purposes. which are mostly oxidised at the expense of oxygen or alternative electron acceptors (aerobic/anaerobic respiration). carbon dioxide fixation). Heterotrophic bacteria include parasitic types. This leads to the ecologically important processes of denitrification. . oxygen is used as the electron acceptor. or autotrophic. or Nitrospirae Organotrophs Organic compounds Organic compounds (chemoheterotrophs) or carbon fixation (chemoautotrophs) Bacillus. anthrax can be contracted by the inhalation of Bacillus anthracis endospores. The distribution of metabolic traits within a group of bacteria has traditionally been used to define their taxonomy. Metabolism Further information: Microbial metabolism Bacteria exhibit an extremely wide variety of metabolic types. sulfate reduction.Bacteria 8 dormant state. This reaction releases energy that can be used to synthesise ATP and drive metabolism. Clostridium or Enterobacteriaceae Carbon metabolism in bacteria is either heterotrophic. "There are viable bacterial spores that have been found that are 40 million years old on Earth — and we know they're very hardened to radiation. the use of chemical substances for energy. green sulfur-bacteria and some purple bacteria. In anaerobic organisms other inorganic compounds. or Purple bacteria Lithotrophs Inorganic compounds Organic compounds (lithoheterotrophs) or carbon fixation (lithoautotrophs) Thermodesulfobacteria. An additional criterion of respiratory microorganisms are the electron acceptors used for aerobic or anaerobic respiration. Chemotrophic organisms use the respective electron donors for energy conservation (by aerobic/anaerobic respiration or fermentation) and biosynthetic reactions (e. Nutritional types in bacterial metabolism Nutritional type Source of energy Source of carbon Examples Phototrophs Sunlight Organic compounds (photoheterotrophs) or carbon fixation (photoautotrophs) Cyanobacteria. the use of light through photosynthesis. such as nitrifying or sulfur-oxidising bacteria. According to scientist Dr.. such as nitrate. respectively." Endospore-forming bacteria can also cause disease: for example. but these traits often do not correspond with modern genetic classifications.g. In Filaments of photosynthetic cyanobacteria aerobic organisms. Bacterial metabolism is classified into nutritional groups on the basis of three major criteria: the kind of energy used for growth. Typical autotrophic bacteria are phototrophic cyanobacteria. Fermentation is possible. two identical clone daughter cells are produced. ferrous iron and other reduced metal ions. Most lithotrophic organisms are autotrophic. because the energy content of the substrates is higher than that of the products. the process used by eukaryotic cells to engulf external items. the gas methane can be used by methanotrophic bacteria as both a source of electrons and a substrate for carbon anabolism. Some bacteria. which is compared to mitosis and meiosis in this image. In both aerobic phototrophy and chemolithotrophy. sulfate-reducing bacteria are largely responsible for the production of the highly toxic forms of mercury (methyl. Bacteria grow to a fixed size and then reproduce through binary fission. butyric acid). for example.Bacteria 9 Another way of life of chemotrophs in the absence of possible electron acceptors is fermentation.. Under optimal conditions. whereas under anaerobic conditions inorganic compounds are used instead.g. form more complex reproductive structures that help disperse the newly formed daughter cells. Examples include fruiting body formation by Myxobacteria and aerial hyphae formation by Streptomyces.and dimethylmercury) in the environment. Budding involves a cell forming a protrusion that breaks away and produces a daughter cell. and bacterial populations can double as quickly as every 9. This environmentally important trait can be found in bacteria of nearly all the metabolic types listed above. a form of asexual reproduction. Many bacteria reproduce through binary fission. while still reproducing asexually. . some bacteria also fix nitrogen gas (nitrogen fixation) using the enzyme nitrogenase. In addition to fixing carbon dioxide in photosynthesis. ammonia (leading to nitrification). Common inorganic electron donors are hydrogen. which enter the cell by diffusion or through molecular channels in cell membranes. The Planctomycetes are the exception (as they are in possessing membranes around their nuclear material). carbon monoxide. hydrogen. ethanol. oxygen is used as a terminal electron acceptor.8 minutes. secreting metabolic by-products (such as ethanol in brewing) as waste. In cell division. whereas organotrophic organisms are heterotrophic. lactate. bacteria can grow and divide extremely rapidly. which allows the organisms to synthesise ATP and drive their metabolism. Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves. increases in cell size (cell growth and reproduction by cell division) are tightly linked in unicellular organisms. Regardless of the type of metabolic process they employ. Non-respiratory anaerobes use fermentation to generate energy and reducing power. the majority of bacteria are able to take in raw materials only in the form of relatively small molecules. It has recently been shown that Gemmata obscuriglobus is able to take in large molecules via a process that in some ways resembles endocytosis. and several reduced sulfur compounds. In unusual circumstances. Growth and reproduction Further information: Bacterial growth Unlike in multicellular organisms. or budding. but is not universal. These processes are also important in biological responses to pollution. Lithotrophic bacteria can use inorganic compounds as a source of energy. wherein the electrons taken from the reduced substrates are transferred to oxidised intermediates to generate reduced fermentation products (e. meaning that bacteria cannot continue to reproduce indefinitely. Solid growth media such as agar plates are used to isolate pure cultures of a bacterial strain. such as the formation of algal (and cyanobacterial) blooms that often occur in lakes during the summer. Genetic changes in bacterial genomes come from either random mutation during replication or "stress-directed . antioxidant metabolism and nutrient transport.Bacteria 10 In the laboratory. a period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. these are much more rare than in eukaryotes. However. The log phase is marked by rapid exponential growth. Other organisms have adaptations to harsh environments. all bacteria can evolve by selection on changes to their genetic material DNA caused by genetic recombination or mutations. The genes in bacterial genomes are usually a single continuous stretch of DNA and although several different types of introns do exist in bacteria.g.000 base pairs in the endosymbiotic bacteria Candidatus Carsonella ruddii. The use of selective media (media with specific nutrients added or deficient. Most laboratory techniques for growing bacteria use high levels of nutrients to produce large amounts of cells cheaply and quickly. A colony of Escherichia coli Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth. However. inherit identical copies of their parent's genes (i. The cells reduce their metabolic activity and consume non-essential cellular proteins. to 12.. such as the production of multiple antibiotics by Streptomyces that inhibit the growth of competing microorganisms. The second phase of growth is the log phase. Bacteria. or with antibiotics added) can help identify specific organisms. which are small extra-chromosomal DNAs that may contain genes for antibiotic resistance or virulence factors. making the cultures easy to divide and transfer. in natural environments. The rate at which cells grow during this phase is known as the growth rate (k). During log phase. Genetics Further information: Plasmid. as asexual organisms. biofilms) that may allow for increased supply of nutrients and protection from environmental stresses. Some organisms can grow extremely rapidly when nutrients become available.200. Mutations come from errors made during the replication of DNA or from exposure to mutagens. liquid growth media are used when measurement of growth or large volumes of cells are required. they are clonal).e. nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The final phase is the death phase where the bacteria runs out of nutrients and dies. The lag phase has high biosynthesis rates. However. Spirochaetes of the genus Borrelia are a notable exception to this arrangement. Mutation rates vary widely among different species of bacteria and even among different clones of a single species of bacteria. bacteria are usually grown using solid or liquid media. also known as the logarithmic or exponential phase. Growth in stirred liquid media occurs as an even cell suspension. In nature. and the time it takes the cells to double is known as the generation time (g).000 base pairs in the soil-dwelling bacteria Sorangium cellulosum. This nutrient limitation has led the evolution of different growth strategies (see r/K selection theory). as proteins necessary for rapid growth are produced.. the cause of Lyme disease. many organisms live in communities (e. with bacteria such as Borrelia burgdorferi. The third phase of growth is the stationary phase and is caused by depleted nutrients. Bacteria may also contain plasmids. the cells need to adapt to their new environment. containing a single linear chromosome. although isolating single bacteria from liquid media is difficult. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repair. These relationships can be essential for growth of a particular organism or group of organisms (syntrophy). The first phase of growth is the lag phase. nutrients are limited. Genome Most bacteria have a single circular chromosome that can range in size from only 160. it must first enter a special physiological state termed competence (see Natural competence). Many types of bacteriophage exist. which allows them to block virus replication through a form of RNA interference. It is seldom that a conjugative plasmid integrates into the host bacterial chromosome. in a process called transformation. where genes involved in a particular growth-limiting process have an increased mutation rate. whereby DNA is transferred through direct cell contact. The length of DNA transferred during B. This can occur in three main ways. bacteria can take up exogenous DNA from their environment. and thus far at least 60 species are known to have the natural ability to become competent for transformation. in the much-studied E. Bacteria resist phage infection through restriction modification systems that degrade foreign DNA. while others insert into the bacterial chromosome. depends on numerous bacterial gene products that specifically interact to perform this complex process. Bacteriophages Main article: Bacteriophage Bacteriophages are viruses that infect bacteria. Transformation. Transduction of bacterial genes by bacteriophage appears to be a consequence of infrequent errors during intracellular assembly of virus particles. 11 . take up and recombine donor DNA into its own chromosome. Genes can also be transferred by the process of transduction. the toxin genes in an integrated phage converted a harmless ancestral bacterium into a lethal pathogen. Plasmid-mediated transfer of host bacterial DNA also appears to be an accidental process rather than a bacterial adaptation. but occasionally transfer may occur between individuals of different bacterial species and this may have significant consequences. The third method of gene transfer is conjugation.Bacteria mutation". Gene transfer is particularly important in antibiotic resistance as it allows the rapid transfer of resistance genes between different pathogens. Conjugation. subtilis transformation can be between a third of a chromosome up to the whole chromosome. in the evolution of Escherichia coli O157:H7 and Clostridium botulinum. and transformation involve transfer of DNA between individual bacteria of the same species. when the integration of a bacteriophage introduces foreign DNA into the chromosome. unlike transduction or conjugation. and thus transformation is clearly a bacterial adaptation for DNA transfer. and is an adaptation for transferring copies of the plasmid from one bacterial host to another. This CRISPR system provides bacteria with acquired immunity to infection. and a system that uses CRISPR sequences to retain fragments of the genomes of phage that the bacteria have come into contact with in the past. coli system is determined by plasmid genes. conjugation. rather than a bacterial adaptation.[5] In ordinary circumstances. some simply infect and lyse their host bacteria. In such cases. gene acquisition from other bacteria or the environment is called horizontal gene transfer and may be common under natural conditions. DNA transfer Some bacteria also transfer genetic material between cells. Transformation appears to be common among bacterial species. and subsequently transfers part of the host bacterial DNA to another bacterium. First. In Bacillus subtilis about 40 genes are required for the development of competence. In order for a bacterium to bind. A bacteriophage can contain genes that contribute to its host's phenotype: for example. such as the transfer of antibiotic resistance. The development of competence in nature is usually associated with stressful environmental conditions. transduction. and seems to be an adaptation for facilitating repair of DNA damage in recipient cells. bacteria in biofilms can have more than 500 times increased resistance to antibacterial agents than individual "planktonic" bacteria of the same species. The secretions are often proteins and may act as enzymes that digest some form of food in the environment. and enables them to produce.[6] Multicellularity See also: Prokaryote § Sociality Bacteria often function as multicellular aggregates known as biofilms. accessing resources that cannot effectively be utilized by single cells. One type of inter-cellular communication by a molecular signal is called quorum sensing. exchanging a variety of molecular signals for inter-cell communication.Bacteria Behavior Secretion Bacteria frequently secrete chemicals into their environment in order to modify it favorably. and engaging in coordinated multicellular behavior. and the light probably serves to attract fish or other large animals. collectively defending against antagonists. as in excreting digestive enzymes or emitting light. and optimizing population survival by differentiating into distinct cell types. This bioluminescence often occurs in bacteria that live in association with fish. The communal benefits of multicellular cooperation include a cellular division of labor. For example. which serves the purpose of determining whether there is a local population density that is sufficiently high that it is productive to invest in processes that are only successful if large numbers of similar organisms behave similarly. Quorum sensing allows bacteria to coordinate gene expression. Bioluminescence Further information: Milky seas effect A few bacteria have chemical systems that generate light. 12 . release and detect autoinducers or pheromones which accumulate with the growth in cell population. The tumbling allows them to reorient and makes their movement a three-dimensional random walk. It is Flagellum of Gram-negative Bacteria. Many bacteria (such as E. coli) have two distinct modes of movement: forward movement (swimming) and tumbling. also now clear. Pilus Many bacteria can move using a variety of mechanisms: flagella are used for swimming through fluids.Bacteria 13 Movement Further information: Chemotaxis. Swimming bacteria frequently move near 10 body lengths per second and a few as fast as 100. Flagellum. repeatedly extending it. both morphologically and genetically. that twitching motility and social gliding motility. The myxobacteria . bacterial gliding and twitching motility move bacteria across surfaces.) The flagella of a unique group of bacteria. while others have flagella distributed over the entire surface of the cell (peritrichous). some have a single flagellum (monotrichous). on a relative scale. such as occurs in Myxococcus xanthus. the myxobacteria.[9] Bacterial species differ in the number and arrangement of flagella on their surface. The bacterial flagella is the best-understood motility structure in any organism and is made of about 20 proteins. In one peculiar group. are essentially the same process. The base drives the rotation of the hook and filament. energy taxis.[7] In bacterial gliding and twitching motility. a flagellum at each end (amphitrichous). This motor drives the motion of the filament. forms appropriate at human-size scale. (See external links below for link to videos. This makes them at least as fast as fish. individual bacteria move together to form waves of cells that then differentiate to form fruiting bodies containing spores. Whitchurch & Mattick (1999) [8] Flagella are semi-rigid cylindrical structures that are rotated and function much like the propeller on a ship. The flagellum is a rotating structure driven by a reversible motor at the base that uses the electrochemical gradient across the membrane for power. and magnetotaxis. and changes of buoyancy allow vertical motion. which acts as a propeller. They have a distinctive helical body that twists about as it moves. Motile bacteria are attracted or repelled by certain stimuli in behaviors called taxes: these include chemotaxis. paddle-like. phototaxis. with approximately another 30 proteins required for its regulation and assembly. Objects as small as bacteria operate a low Reynolds number and cylindrical forms are more efficient than the flat. are found between two membranes in the periplasmic space. the spirochaetes." —"A re-examination of twitching motility in Pseudomonas aeruginosa" – Semmler. bacteria use their type IV pili as a grappling hook. "Our observations redefine twitching motility as a rapid. clusters of flagella at the poles of the cell (lophotrichous). highly organized mechanism of bacterial translocation by which Pseudomonas aeruginosa can disperse itself over large areas to colonize new territories. anchoring it and then retracting it with remarkable force (>80 pN). pigments. Classification of bacteria is determined by publication in the International Journal of Systematic Bacteriology. antigens and quinones. which is motile in liquid or solid media. bacterial classification remains a changing and expanding field. and Bergey's Manual of Systematic Bacteriology. they can form a kind of tail that pushes them through the host cell's cytoplasm. Classification and identification Main article: Bacterial taxonomy Further information: Scientific classification. These two domains.Bacteria move only when on solid surfaces. such as the rRNA gene. unlike E. Identification of bacteria in the laboratory is particularly relevant in medicine. which is currently the most widely used classification system in microbiolology. but now called Bacteria and Archaea that evolved independently from an ancient common ancestor. For example. However. are the basis of the three-domain system. it was unclear whether these Streptococcus mutans visualized with a Gram stain differences represented variation between distinct species or between strains of the same species. While these schemes allowed the identification and classification of bacterial strains. where the correct treatment is determined by the bacterial species causing an infection. Bacteria can be classified on the basis of cell structure. Due to lateral gene transfer. Consequently. molecular systematics showed prokaryotic life to consist of two separate domains. The term "bacteria" was traditionally applied to all microscopic. By promoting actin polymerization at one pole of their cells. The International Committee on Systematic Bacteriology (ICSB) maintains international rules for the naming of bacteria and taxonomic categories and for the ranking of them in the International Code of Nomenclature of Bacteria. originally called Eubacteria and Archaebacteria. 14 . some closely related bacteria can have very different morphologies and metabolisms. cellular metabolism or on differences in cell components such as DNA. coli. using genetic techniques such as guanine cytosine ratio determination. This uncertainty was due to the lack of distinctive structures in most bacteria. Systematics. To overcome this uncertainty. a few biologists argue that the Archaea and Eukaryotes evolved from Gram-positive bacteria. along with Eukarya. fatty acids. The archaea and eukaryotes are more closely related to each other than either is to the bacteria. the need to identify human pathogens was a major impetus for the development of techniques to identify bacteria. Bacterial phyla and Clinical pathology Classification seeks to describe the diversity of bacterial species by naming and grouping organisms based on similarities. genome-genome hybridization. as well as sequencing genes that have not undergone extensive lateral gene transfer. single-cell prokaryotes. modern bacterial classification emphasizes molecular systematics. due to the relatively recent introduction of molecular systematics and a rapid increase in the number of genome sequences that are available. as well as lateral gene transfer between unrelated species. However. Several Listeria and Shigella species move inside host cells by usurping the cytoskeleton. which is normally used to move organelles inside the cell. Often these techniques are designed for specific specimens. the total number of bacterial species is not known and cannot even be estimated with any certainty. Specimens that are normally sterile. and staining.. it can be further characterised by its morphology. 15 . while stool specimens are cultured on selective media to identify organisms that cause diarrhoea. while the thin "Gram-negative" cell wall appears pink. there are a little less than 9. such as serology. but attempts to estimate the true number of bacterial diversity have ranged from 107 to 109 total species – and even these diverse estimates may be off by many orders of magnitude. even using these improved methods. archaea green and organisms are best identified by stains bacteria blue. are cultured under conditions designed to grow all possible organisms.. growth patterns (such as aerobic or anaerobic growth). which show acid-fastness on Ziehl–Neelsen or similar stains. such as blood. Diagnostics using such DNA-based tools. As with bacterial classification. Gram-negative cocci and Gram-negative bacilli). The thick layers of peptidoglycan in the "Gram-positive" cell wall stain purple. other than the Gram stain. Other organisms may need to be identified by their growth in special media. most bacteria can be classified as belonging to one of four groups (Gram-positive cocci. urine or spinal fluid. Some bibcode = 2006Sci. characterises bacteria based on the structural characteristics of their cell walls. Following present classification. patterns of hemolysis. while preventing growth of non-pathogenic bacteria. or by other techniques.Bacteria The Gram stain. However. particularly mycobacteria or Nocardia.1283C }}</ref> Eukaryotes are colored red.300 known species of prokaryotes. while restricting the growth of the other bacteria in the sample. Gram-positive bacilli. a sputum sample will be treated to identify organisms that cause pneumonia. for example.311. By combining morphology and Gram-staining. Culture techniques are designed to promote the growth and identify particular bacteria. are increasingly popular due to their specificity and speed. such as polymerase chain reaction. identification of bacteria is increasingly using molecular methods. These methods also allow the detection and identification of "viable but nonculturable" cells that are metabolically active but non-dividing. compared to culture-based methods. Once a pathogenic organism has been isolated. which includes bacteria and archaea. developed in 1884 by Hans Christian Gram. their growth can be increased by warmth and sweat. Many other bacteria are found as symbionts in humans and other organisms. Only the intimate association with the hydrogen-consuming Archaea keeps the hydrogen concentration low enough to allow the bacteria to grow. In soil. converting nitrogen gas to nitrogenous compounds. foodborne illness. A pathogenic cause for a known medical disease may only be discovered many years after. Pathogens Main article: Pathogenic bacteria If bacteria form a parasitic association with other organisms. These predatory bacteria are thought to have evolved from saprophages that consumed dead microorganisms. these species called predatory bacteria. leprosy and tuberculosis. These include organisms such as Myxococcus xanthus.Bacteria 16 Interactions with other organisms Despite their apparent simplicity. Pathogenic bacteria are a major cause of human death and disease and cause infections such as tetanus. typhoid fever. Due to their small size. vitamin K and biotin. and methanogenic Archaea that consume hydrogen. Predators Some species of bacteria kill and then consume other microorganisms. such as Vampirococcus. convert sugars to lactic acid (see Lactobacillus). which forms swarms of cells that kill and digest any bacteria they encounter. The bacteria in this association are unable to consume the organic acids as this reaction produces hydrogen that accumulates in their surroundings. they are classed as pathogens. mutualism and commensalism. bacteria can form complex associations with other organisms. the presence of over 1. commensal bacteria are ubiquitous and grow on animals and plants exactly as they will grow on any other surface. For example. called interspecies hydrogen transfer. which cannot fix nitrogen themselves. Bacterial diseases are also important in agriculture. and large populations of these organisms in humans are the cause of body odor. syphilis. as well as Johne's disease. Color-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells . salmonella and anthrax in farm animals. fire blight and wilts in plants. occurs between clusters of anaerobic bacteria that consume organic acids such as butyric acid or propionic acid and produce hydrogen. as was the case with Helicobacter pylori and peptic ulcer disease. Other bacterial predators either attach to their prey in order to digest them and absorb nutrients. These symbiotic associations can be divided into parasitism. This serves to provide an easily absorbable form of nitrogen for many plants. However. as well as fermenting complex undigestible carbohydrates. The presence of this gut flora also inhibits the growth of potentially pathogenic bacteria (usually through competitive exclusion) and these beneficial bacteria are consequently sold as probiotic dietary supplements. Mutualists Certain bacteria form close spatial associations that are essential for their survival. or invade another cell and multiply inside the cytosol.000 bacterial species in the normal human gut flora of the intestines can contribute to gut immunity. cholera. diphtheria. with bacteria causing leaf spot. through adaptations that allowed them to entrap and kill other organisms. mastitis. synthesise vitamins such as folic acid. such as Daptobacter. One such mutualistic association. microorganisms that reside in the rhizosphere (a zone that includes the root surface and the soil that adheres to the root after gentle shaking) carry out nitrogen fixation. Chlamydia. Other organisms invariably cause disease in humans. sauerkraut. One species of Rickettsia causes typhus.Bacteria Each species of pathogen has a characteristic spectrum of interactions with its human hosts. Surgical and dental instruments are also sterilized to prevent contamination by bacteria. soy sauce. some species such as Pseudomonas aeruginosa. which are obligate intracellular parasites able to grow and reproduce only within the cells of other organisms. pneumonia. which are classified as bacteriocidal if they kill bacteria. Burkholderia cenocepacia. often lactic acid bacteria such as Lactobacillus and Lactococcus. or urinary tract infection and may be involved in coronary heart disease. where they may be contributing to the rapid development of antibiotic resistance in bacterial populations. can cause skin infections. have been used for thousands of years in the preparation of fermented foods such as cheese. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills. vinegar. wine and yogurt. such as the Rickettsia. which inhibit the bacterial ribosome. contains species that can cause pneumonia. Significance in technology and industry Further information: Economic importance of bacteria Bacteria. and Mycobacterium avium are opportunistic pathogens and cause disease mainly in people suffering from immunosuppression or cystic fibrosis. and by proper care of indwelling catheters. such as Staphylococcus or Streptococcus. An example of how antibiotics produce selective toxicity are chloramphenicol and puromycin. Infections can be prevented by [10] Overview of bacterial infections and main species involved. pickles. Bacteria are also used for the bioremediation of industrial toxic 17 . but not the structurally different eukaryotic ribosome. Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection. while another causes Rocky Mountain spotted fever. The ability of bacteria to degrade a variety of organic compounds is remarkable and has been used in waste processing and bioremediation. Fertilizer was added to some of the beaches in Prince William Sound in an attempt to promote the growth of these naturally occurring bacteria after the 1989 Exxon Valdez oil spill. Some organisms. There are many types of antibiotics and each class inhibits a process that is different in the pathogen from that found in the host. Yet these organisms are also part of the normal human flora and usually exist on the skin or in the nose without causing any disease at all. Bacterial infections may be treated with antibiotics. another phylum of obligate intracellular parasites. or bacteriostatic if they just prevent bacterial growth. antiseptic measures such as sterilizing the skin prior to piercing it with the needle of a syringe. Antibiotics are used both in treating human disease and in intensive farming to promote animal growth. meningitis and even overwhelming sepsis. a systemic inflammatory response producing shock. massive vasodilation and death. Finally. in combination with yeasts and molds. These efforts were effective on beaches that were not too thickly covered in oil. enzymes and metabolic pathways in bacteria. In the chemical industry. Pasteur was an early advocate of the germ theory of disease. bacteria are the workhorses for the fields of molecular biology. scientists can determine the function of genes. Bacteria were first observed by the Dutch microscopist Antonie van Leeuwenhoek in 1676. for which he received a Nobel Prize in 1905. By making mutations in bacterial DNA and examining the resulting phenotypes. Bacteria can also be used in the place of pesticides in the biological pest control. This commonly involves Bacillus thuringiensis (also called BT). This understanding of bacterial metabolism and genetics allows the use of biotechnology to bioengineer bacteria for the production of therapeutic proteins. He then published his observations in a series of letters to the Royal Society of London.[13] Antonie van Leeuwenhoek. a genus of spore-forming rod-shaped bacteria defined by Ehrenberg in 1835. bacteria are most important in the production of enantiomerically pure chemicals for use as pharmaceuticals or agrichemicals.) Along with his contemporary Robert Koch. Subspecies of this bacteria are used as a Lepidopteran-specific insecticides under trade names such as Dipel and Thuricide. genetics and biochemistry. In 1910. pollinators and most other beneficial insects. This is achievable in some well-studied bacteria. such as insulin. a pioneer in medical microbiology. Because of their ability to quickly grow and the relative ease with which they can be manipulated. soil dwelling bacterium. and these postulates are still used today. In Koch's postulates. with models of Escherichia coli metabolism now being produced and tested. Though it was known in the nineteenth century that bacteria are the cause of many diseases. no one else would see them again for over a century. Louis Pasteur demonstrated in 1859 that the growth of microorganisms causes the fermentation process. In his research into tuberculosis Koch finally proved the germ theory. Robert Koch. using a single-lens microscope of his own design. the first microbiologist and the first person to observe bacteria using a microscope. see Microbiology. no effective antibacterial treatments were available. his Bacterium was a genus that contained non-spore-forming rod-shaped bacteria. (Yeasts and molds. a Gram-positive. these pesticides are regarded as environmentally friendly. commonly associated with fermentation. in one of the most striking hiatuses in the history of science. as opposed to Bacillus.Bacteria 18 wastes. Bacteria were Leeuwenhoek's most remarkable microscopic discovery.[12] In fact. but rather fungi. Because of their specificity. This aim of understanding the biochemistry of a cell reaches its most complex expression in the synthesis of huge amounts of enzyme kinetic and gene expression data into mathematical models of entire organisms. For the natural history of Bacteria.[11] Only then were his by-then-largely-forgotten observations of bacteria — as opposed to his famous "animalcules" (spermatozoa) — taken seriously. History of bacteriology For the history of microbiology. Paul Ehrlich developed the first antibiotic. with little or no effect on humans. and that this growth is not due to spontaneous generation. see Last universal ancestor. wildlife. by changing dyes that selectively stained Treponema pallidum — the spirochaete that causes syphilis — into compounds that selectively killed the . For the history of bacterial classification. anthrax and tuberculosis. or antibodies. see Bacterial taxonomy. They were just at the limit of what his simple lenses could make out and. worked on cholera. then apply this knowledge to more complex organisms. Christian Gottfried Ehrenberg introduced the word "bacterium" in 1828. are not bacteria. he set out criteria to test if an organism is the cause of a disease. growth factors. with his work being the basis of the Gram stain and the Ziehl–Neelsen stain. ISBN 978-1-62100-808-8. Retrieved on 11 April 2009 [11] Asimov. ISBN 0-7167-5060-0. Animalia evertebrata. (2006). (2009).J. Louis: Mosby. Berlin: Springer. N. • Atlas RM (1995). pg 143.org/ftl/cgi-bin/ftl?st=&su=Bacteria&library=OLBP) Resources in your library (http://tools. Bernstein C. Michod RE (2012).. and pioneered the use of stains to detect and identify bacteria. Garden City.nih. This new phylogenetic taxonomy depended on the sequencing of 16S ribosomal RNA. lef. • Martinko JM. David B. [13] EHRENBERG (C. PMID 9733676 (http://www. "Impact of culture-independent studies on the emerging phylogenetic view of bacterial diversity" (http://jb. Pace NR (15 September 1998).Bacteria 19 pathogen. [10] LEF. ISBN 0-7637-1067-9. (1996). Goebel BM.G. eds. Harvard University Press. San Francisco: Benjamin Cummings.ncbi. Chapter 1: pp. full [9] Dusenbery. Mass. References [1] http:/ / science. Ehrlich had been awarded a 1908 Nobel Prize for his work on immunology. [12] Ehrenberg's Symbolae Physioe. (2009). National Council for Science and the Environment. Harvard University Press. • Holt JC. Sakura Kimura and Sora Shimizu (eds. St. Scientific American Library. eoearth.Michael Hogan. David B. pp.). com/ view/ entry/ m_en_gb0055310#dws-m_en_gb-m-en_gb-msdict-00002â034344). ISBN 0-8016-7790-4. (2009). ISBN 0-8053-7614-3. Further reading Library resources about Bacteria • • • Online books (http://tools. Jessup M. Cambridge. [5] Bernstein H. • Funke BR. Tortora GJ. [8] http:/ / mic. ISBN 3-540-32524-7.nlm. ISBN 978-0-674-03116-6. 1835. pp. Mass. • Hugenholtz P. nasa. Isaac (1982). Chapter 13.): Dritter Beitrag zur Erkenntniss grosser Organisation in der Richtung des kleinsten Raumes. J Bacteriol 180 (18): 4765–74. Living at Micro Scale.asm. N. Microbiology: an introduction (8th ed. ISBN 978-0-674-03116-6.wmflabs.nlm. gov/ science-news/ science-at-nasa/ 2007/ 11may_locad3/ [2] C.org > Bacterial Infections (http:/ / www. Complex Intracellular Structures in Prokaryotes (Microbiology Monographs). Fundamentals of microbiology.org/cgi/content/full/180/18/ 4765?view=full&pmid=9733676). [4] Dusenbery.).wmflabs.org/ftl/cgi-bin/ftl?st=&su=Bacteria&library=0CHOOSE0) • Alcamo IE (2001). Principles of microbiology.). sgmjournals. 143–336. 2nd edition. [6] Dusenbery. PMC 107498 (http://www. Englewood Cliffs. Cambridge.Cleveland. 1–49 in: DNA Repair: New Research. "DNA repair as the primary adaptive function of sex in bacteria and eukaryotes". htm) Updated: 19 January 2006. [7] Dusenbery. Brock Biology of Microorganisms (11th ed. Decas prima.org/ftl/cgi-bin/ftl?st=&su=Bacteria) Resources in other libraries (http://tools. 2010. Bergey's manual of determinative bacteriology (9th ed. p. 1828. 20–25. Publ. New York: Doubleday and Company. and divided prokaryotes into two evolutionary domains.gov/pubmed/9733676). ISBN 978-0-674-03116-6.J: Prentice Hall. Harvard University Press. gov/pmc/articles/PMC107498). Madigan MT (2005).wmflabs. ISBN 0-683-00603-7. Case CL (2004). Bacteria. Living at Micro Scale. Cambridge. Physikalische Abhandlungen der Koeniglichen Akademie der Wissenschaften zu Berlin aus den Jahren 1833–1835. Living at Micro Scale. Hauppauge. A major step forward in the study of bacteria came in 1977 when Carl Woese recognized that archaea have a separate line of evolutionary descent from bacteria. Encyclopedia of Earth. org/ protocols/ infections/ bacterial_infection_01. . David B.Y.ncbi. Sidney Draggan and C. Washington DC (http:/ / www. David B. Mass. Berlin. Asimov's Biographical Encyclopedia of Science and Technology.nih. Bergey DH (1994). 136. on Oxford Dictionaries. Baltimore: Williams & Wilkins. Boston: Jones and Bartlett. org/ content/ 145/ 10/ 2863. Life at Small Scale. • Shively. org/ article/ Bacteria?topic=49480) [3] bacterium (http:/ / oxforddictionaries. as part of the three-domain system.). Nova Sci. ISBN 0-13-144329-1. bacteria) • PATRIC (http://patricbrc.htm) • Tree of Life: Eubacteria (http://tolweb.bacterio.harvard.edu/index.php/Viral_Biorealm) • Bacteria that affect crops and other plants (http://www.niaid. (http://www. an extensive wiki about bacteria (http://microbewiki.html) of bacteria swimming and tumbling.ted.html) by Stephen Jay Gould • On-line text book on bacteriology (http://www.com/index.org/pages/sn_arc99/4_17_99/fob5.net/) • Animated guide to bacterial cell structure.dsmz.php/MicrobeWiki).nih.kenyon.com/trun/artwork/Animations/ Overview/overview.textbookofbacteriology. use of optical tweezers and other videos. and TED: Discovering bacteria's amazing communication system (http://www.ncppb.edu/labs/bacteria/index_movies.stephenjaygould.fr/eubacteria.de/bactnom/bactname.gov/) • Bacterial Chemotaxis Interactive Simulator (http://wormweb.org/tree?group=Eubacteria&contgroup=Life_on_Earth) • Videos (http://www.html) Library resources about Bacteria • Resources in your library (http://tools.org/ftl/cgi-bin/ftl?st=wp&su=Bacteria) . edu/index.Bacteria 20 External links Wikispecies has information related to: Bacteria • MicrobeWiki (http://microbewiki.kenyon.php/Microbial_Biorealm) and viruses (http://microbewiki.edu/index.blackwellpublishing.newscientist.wmflabs.cict.org/). funded by NIAID (http://www.htm) • Genera of the domain Bacteria (http://www.com/articles/2009/02/19/online. php/talks/bonnie_bassler_on_how_bacteria_communicate.org/ibioseminars/Bassler/Bassler1.html) • Online collaboration for bacterial taxonomy. • Planet of the Bacteria (http://www. a Bioinformatics Resource Center for bacterial pathogens. collaboration. • Cell-Cell Communication in Bacteria (http://ascb.org/library/gould_bacteria.html) • Bacteria Make Major Evolutionary Shift in the Lab (http://www.org/bacteriachemo) – A web-app that uses several simple algorithms to simulate bacterial chemotaxis.identifies.kenyon.sciencenews.html) – list of Prokaryotic names with Standing in Nomenclature • The largest bacteria (http://www.com) • Bacterial Nomenclature Up-To-Date from DSMZ (http://www.com/channel/life/ dn14094-bacteria-make-major-evolutionary-shift-in-the-lab.rowland. 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