General Characteristics of Bacteria and Mollicutes

General characteris tics of Bacteria and MollicutesMorphology and Ecology Submitted to : M’am Uzma Bashir Submitted by : Mehra Azam 34 Gul-irayna 42 Iqra Asghar 43 i. one needs to revisit various measurement units. The appendages of cell wall include flagellae -the organs of locomotion and fimbriae which help in adhesion of bacteria. Bacterial cell Introduction to Plant pathogens .e. A bacterium shall characteristically have a cell envelope which includes a layered cell wall and external surface adherents. nuclear apparatus surrounded by an amorphous cytoplasm which contains ribosomes. Internally the bacterium has loose arrangement of DNA. Mesosomes and inclusion granules are other structures present in bacterium. To understand their size. The unit of measurement used in bacteriology is the micron (µ) or also called micrometer (µm). 1 µm = One thousandth of a millimeter.2 General characteristics of bacteria and mollicutes THE BACTERIAL CELL General characteristics of Bacteria and Mollicutes Bacteria cannot be visualized by naked eye. Some of the bacilli also have the tendency to cluster together indifferent patterns but in the absence of any consistency in the patterns it is difficult to assign them anycharacteristic arrangement. Filaments are long threads of bacilli which have not separated into single cells. Apart from the length and width of the bacilli the shape of the ends often shows features that are of differential value. They may be: ➢ Rounded. Cocci are true spheres with diameter ranging between 0. Spirochetes are long curved bacteria with as many as 20 coils.25 µm (and average of 1 µm). ➢ Square cut or ➢ Sharply pointed Arrangement of Bacterial Cells Cocci may occur in pairs as in diplococci. Bacilli varying length from 2-10 times their width.  Cylinderical (bacilli or rods) and  Spirillar (spirochetes).75 to 1.3 General characteristics of bacteria and mollicutes Shape and Size of Bacteria Bacteria can have any of the following three shapes  Spheroidal (cocci). Coccobacilli are very short bacilli. Some of the commonly seen arrangements of bacteria are: Introduction to Plant pathogens . the simplest of microbial cells. which contain a peptidoglycan layer ➢ Tiny. they consist of cell protoplasm contained within a retaining structure or cell envelope. In essence. or unique cell envelopes.4 General characteristics of bacteria and mollicutes Bacteria: The Basics Bacteria are prokaryotic cells. measured in units called micrometers (µm) ➢ ➢ ➢ ➢ Introduction to Plant pathogens . Basic Characteristics: Prokaryotic Simplest of all microbial cells Single-celled organisms Distinctive cell walls. . DNA) ➢ DNA is free floating ➢ May have additional DNA which is not associated with this nucleoid region (called a plasmid) ➢ Rapid growth and cell division (binary fission) under favorable conditions ➢ Mutants that arise from bacteria can become extremely resilient organisms because bacteria can: ○ Grow and reproduce cells quickly ○ Adapt quickly to changing environments ➢ Plasmids impart additional resistant characteristics to bacteria via cellto-cell transfer of this extra DNA material ➢ Capable of colonizing in almost any environment ➢ Extremely diverse and numerous in soils or waters ➢ Morphology of bacterial cell ➢ The overall form of a basic bacterial cell is that of a complex cell envelope that encloses cell protoplasm. instead. have a region called the ‘nucleoid region' (i.e. Constituents of bacterial cell components Introduction to Plant pathogens .5 General characteristics of bacteria and mollicutes Other Characteristics: ➢ Lack a true nucleus. Cell appendages from the envelope protrude into the environment surrounding the cell. In Gram-positive bacteria. others have several polar flagella (lophotrichous). These appendages are outlined below: 1. Counterclockwise rotation of the flagella produces motility in a forward motion. Flagella may Introduction to Plant pathogens . Flagella are composed of flagellins (proteins) that make up the long filament. an additional two rings are found in the outer membrane. Flagella: These are the organs of motility. This filament is connected to a hook and rings that anchor the flagella in the cell wall. Flagella may be up to 20 µm in length. others have several flagella at each end of the cell (amphitrichous). Some bacteria possess a single polar flagellum (monotrichous). there are two rings attached to the cytoplasmic membrane.6 General characteristics of bacteria and mollicutes SURFACE APPENDAGES Bacteria may or may not possess surface appendages that provide the organism with the ability to be motile or to transfer genetic material or to attach to host tissues. clockwise rotation produces a tumbling motion. and still others have many flagella covering the entire cell surface (peritrichious). in Gram-negative cells. epithelial cells) and often play an important role in colonization (e. pyogenes). Other important constituents of the cell wall include the following: ○ Peptidoglycan: This is a polymer of alternating N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG). 2. D-alanine tetrapeptides to NAM. If the layer is strongly adhered to the cell wall.g. if not. Gram-positive cells have a much more highly cross-linked peptidoglycan structure than Gram-negative cells. gonorrhoeae). L-lysine. Pili: These surface appendages come in two distinct forms having distinct purposes. Gram-positive bacteria have a thick layer of peptidoglycan external to the cytoplasmic membrane. This region is known as the periplasmic space. the M protein of S. Gram-negative bacteria have a thin layer of peptidoglycan located between the cytoplasmic membrane and a second membrane called the outer membrane. These structures provide the means for attachment to host cells (e. the H antigens of Gram-negative enteric bacteria).7 General characteristics of bacteria and mollicutes serve as antigenic determinants (e. 1. These polysaccharides extend though the Introduction to Plant pathogens ○ . Common pili: This form of pilus is usually relatively short and many SURFACE LAYERS (about 200) and can be found covering the cell surface. D-glutamic acid. the transfer of genetic information from one cell to another. Pili (or fimbrae) may also provide antigenic determinants (e. 2. 2. Capsules: This type of surface layer is composed primary of high molecular weight polysaccharides. N. These structures can also provide the receptor for certain male-specific bacteriophages. it is called a capsule. These layers provide resistance to phagocytosis and serve as antigenic determinants. penicillins interfere with the enzymes involved in biosynthesis of peptidoglycan while lysozyme physically cleaves the NAM-NAG bond. Long strands of this alternating polymer may be linked by L-alanine.g. These structures are involved in conjugation.g. protruding from the cell surface. The production of capsules is genetically and phenotypically controlled. These layers are outlined below: 1. Cell wall: The cell wall is the basis for classification of bacteria according to the Gram stain. Peptidoglycan is also the "target" of antimicrobial activity. Bacteria possess several distinct surface layers that can enhance their pathogenicity. In contrast.g. it is called a slime layer. Lipoteichoic acids: Lipoteichoic acids (LTA) are found only in Grampositive bacteria. For example. Sex pili: This form of pilus can be relatively long but is often found in few numbers. generally 1 to 6. serving as an antigenic determinant ("O antigen"). they are categorized into Gram-positive and Gram-negative bacteria. This staining technique was developed by Hans Christian Gram. ○ Lipopolysaccharides: Lipopolysaccharides (LPS) are found only in Gram-negative bacteria. which binds the LPS in the outer membrane and is itself the endotoxic portion of the molecule.8 General characteristics of bacteria and mollicutes entire peptidoglycan layer and appear on the cell surface. Gram’s Staining – • • • Based on their cell wall types. As a consequence. This is the most widely used method of bacterial staining and classification. The polysaccharide moiety appears on the cell surface. these structures can serve as antigenic determinants. These structures are composed of lipid A. a Danish physician in the year 1883. shape and arrangement. Identification of bacteria The bacterial cells are stained by simple staining methods to study their size. Characteristics of a Gram-positive bacterium are given below – Introduction to Plant pathogens . The amount of lipid is less in the cell wall. the cell membrane and the cell wall (thick layer of peptidoglycan). help to break down organic material. along with fungi. making the cell wall thick. they think of disease-causing organisms. Ecology of Bacteria -Bacteria contribute in many ways to the ecosystem. This staining method is based on the lipid content of the cell. and decomposers. From these unicellular prokaryotic organisms. Bacteria like nitrogen fixers contribute significantly to the life cycle of living creatures. Characteristics of a Gram-negative bacterium are given below – • • The cell envelop is thin but. Bacteria are among the bottom of many food webs. which retains the stain back in the cell. While some can be harmful to living creatures. the cell wall. eukaryotes evolved and eventually multicellular organisms like us evolved.9 General characteristics of bacteria and mollicutes • • The cell is made of two layers. a thin layer of peptidoglycan) and cell membrane. Thus. like the Streptococcus bacteria growing in culture in this picture. Acid fast staining – Some bacteria need a little harsh methods of treatment for staining. which dissolves in ethanol and washing away the stain. made of three layers. Bacteria grow in a wide variety of habitats and conditions. Large quantities of lipids are present in the cell. -Bacteria were one of the first organisms on the planet. Introduction to Plant pathogens . When most people think of bacteria. we would not be alive if it weren't for the bacteria in our intestines that help us break down food. Bacteria have a wide range of envronmental and nutritive requirements. or other elements (chemoautotrophic). and last so long is their ability to go dormant for an extended period. Organic carbon. Bacteria may also be classified both by the mode by which they obtain their energy. Other bacteria are anaerobic. and cannot tolerate gaseous oxygen. Heterotrophs derive energy from breaking down complex organic compounds that they must take in from the environment -. since they use hydrogen sulfide as hydrogen donor.this includes saprobic bacteria found in decaying material. including cyanobacteria. Bacteria play important roles in the global ecosystem. green sulfur bacteria. Aerobic bacteria thrive in the presence of oxygen and require it for their continued growth and existence. Bacteria are so widespread that it is possible only to make the most general statements about their life history and ecology. such disease-causing species are a comparatively tiny fraction of the bacteria as a whole. would quickly deplete the carbon dioxide in the atmosphere if not for the activity of decomposers. and purple nonsulfur bacteria. nitrogen. and no food. or those which cause bacterial food poisoning. the carbon contained in their tissues becomes unavailble Introduction to Plant pathogens . and sulfur is completed by their ceaseless labor.10 General characteristics of bacteria and mollicutes which were isolated from a man with strep throat. or by oxidation of nitrogen. both on land and in the water. instead of water like most other photosynthetic organisms. When organisms die. The cycling of nutrients such as carbon. but realize that without carbon dioxide. such as those bacteria which live in deep underwater sediments. and gonorrhea. The sulfur bacteria are particularly interesting. purple sulfur bacteria. The other group. bacteria fall into two categories: heterotrophs and autotrophs. but can continue to grow without it. as well as those that rely on fermentation or respiration. The third group are the facultative anaerobes. the bottom of the deepest oceans. sulfur. One feature that has enabled them to spread so far. this may be fueled by light energy (photoautotrophic). They include the cyanobacteria. Most bacteria may be placed into one of three groups based on their response to gaseous oxygen. While pathogenic bacteria are notorious for such diseases as cholera. While chemoautotrophs are uncommon. tuberculosis. in the guts of animals. photoautotrophs are common and quite diverse. depends heavily upon the activity of bacteria. the autotrophs. The ecosystem. This may not sound too bad to you. They may be found on the tops of mountains. Classified by the source of their energy. there would be no photosynthesis in plants. and even in the frozen rocks and ice of Antarctica. in the form of dead and rotting organisms. which prefer growing in the presence of oxygen. fix carbon dioxide to make their own food source. The word "Mollicutes" is derived from the Latin mollis (meaning "soft" or "pliable"). Decomposition is the breakdown of these organisms. and the resulting products are released into the environment. Mollicutes (mycoplasma) The Mollicutes are a class of bacteria distinguished by the absence of a cell wall.11 General characteristics of bacteria and mollicutes for most other living things. Introduction to Plant pathogens .2–0. These bacteria convert gaseous nitrogen into nitrates or nitrites as part of their metabolism. such as liverworts. typically only 0. and make it difficult for crops to grow. Nostoc. they may deplete the soil nutrients. and is one of the most important roles of the bacteria. Individuals are very small. They are parasites of various animals and plants. Other denitrifying bacteria metabolize in the reverse direction. and Spirulina. cycads. Many are able to move about through gliding. turning nitrates into nitrogen gas or nitrous oxide. and cannot acquire it from the gaseous nitrogen in the atmosphere. Some plants. They vary in form. and by cyanobacteria such as Anabaena. and legumes have taken special advantage of this process by modifying their structure to house the basteria in their own tissues. Plants rely on nitrogen from the soil for their health and growth. although most have sterols that make the cell membrane somewhat more rigid. and cutis (meaning "skin"). The cycling of nitrogen is another important activity of bacteria. shown at right.3 μm in size and have a very small genome size. When colonies of these bacteria occur on croplands. and the release of nutrients back into the environment. The best-known genus in Mollicutes is Mycoplasma. living on or in the host's cells. The primary way in which nitrogen becomes available to them is through nitrogen fixation by bacteria such as Rhizobium. but members of the genus Spiroplasma are helical and move by twisting. and is implicated in normal cell division. Mycoplasmas generally possess a relatively small genome of 0. one • • • • of several genera within the bacterial class Mollicutes. possess a polar extension protruding from the pseudococcoidal cell body. the cells often present a certain shape. including M. usually as cholesterol from the animal host. Species of the M. Despite this. Sterols are acquired from the environment. 37° C in humans) or ambient temperature if the host is unable to regulate its own internal temperature. pneumoniae cells are pleomorphic. whereas other species in the cluster typically lack the trailing filament. Mollicutes are parasites or commensals of humans.58-1. and plants. is essential for adherence to host cells and for movement along solid surfaces (gliding motility). with a characteristic small size. Analysis of 16S ribosomal RNA sequences as well as gene content strongly suggest that the mollicutes. including the mycoplasmas. Species of the M. Cell morphology The bacteria of the genus Mycoplasma (trivial name: mycoplasmas) and their close relatives are characterized by lack of a cell wall. M. Their optimum growth temperature is often the temperature of their host if warmbodied (e. are closely related to either the Lactobacillus or the Clostridium branch of the phylogenetic tree (Firmicutes sensu stricto). g. designated an attachment organelle or terminal organelle. which results in drastically reduced biosynthetic capabilities and explains their dependence on a host. This tip structure. with typically about 10% of the volume of an Escherichia coli cell.12 General characteristics of bacteria and mollicutes Characteristics • There are over 100 recognized species of the genus Mycoplasma. Most are pseudococcoidal. pneumoniae cluster. These cell shapes presumably contribute to the ability of mycoplasmas to thrive in their respective environments. the genus Mycoplasma is by definition restricted to vertebrate hosts. They have a low GC-content (23-40 mol %). mobile and M. fastidiosum cluster are rod-shaped. Cholesterol is required for the growth of species of the genus Mycoplasma as well as certain other genera of mollicutes. but there are notable exceptions. with an attachment organelle of regular dimensions at one pole and a trailing filament of variable length and uncertain function at the other end.38 megabases. Additionally they use an alternate genetic code where the codon UGA is encoding for the amino acid tryptophan instead of the usual opal stop codon. pulmonis have similar structures with similar functions. Introduction to Plant pathogens . Mycoplasmas are unusual among bacteria in that most require sterols for the stability of their cytoplasmic membrane. Other species like M. other animals (including insects). pneumoniae. relatively close contact is required for transmission to occur. Introduction to Plant pathogens . coughing animal. Contagious bovine pleuropneumonia is spread by inhalation of droplets from an infected. They rely on their hosts for much of their nutrition mainly due to fact that they have a degraded genome and are not able to perform many basic functions of most bacteria. However.13 General characteristics of bacteria and mollicutes Ecology Mycoplasma mycoides are parasites that can be found predominantly in cattle and goat hosts.