Bacteria: Bacterial Morphology and Structure PDF

3- Bacteria Bacteria are small microorganisms, generally unicellular although the cells may grow as filaments e.g. the higher bacteria (the actinomycetes). The cells are usually between 0.4 and 1.5u in diameter. They are prokaryotic i.e. are morphologically less complicated than the eucaryotic c...

3- Bacteria Bacteria are small microorganisms, generally unicellular although the cells may grow as filaments e.g. the higher bacteria (the actinomycetes). The cells are usually between 0.4 and 1.5u in diameter. They are prokaryotic i.e. are morphologically less complicated than the eucaryotic cells of higher organisms because they lack a nuclear membrane, a mitotic apparatus, mitochondria, and visible endoplasmic reticulum. Fig. (8) Different forms of bacteria 1. Morphology: Bacteria possess 3main forms which are spherical (cocci), rod-shaped (bacilli and clostridia) and spiral- shaped ( vibriones and spirilla). A- Cocci. Include spherical. it is subdivided into six groups according to the cell arrangement, cell division and biological properties. 1- Micrococci: Single cells. 2-Diplococci: The cell divides in one plane and the pairs remain attached. 3-Tetracocci: the cell divides in 2 planes at right angles to one another "resulting in the formation of groups of fours. 4-Sarcina:- The cell divides in three planes at right angles to one another and resemble packets or cubes of 8, 16 or more cells. 5- Streptococci Division of cell is in one plane and are arranged in chains of different lengths. 6- Staphylococci Division occurs in several planes resulting in irregular bunches of cells, resembling clusters of graphs.  B- Bacilli. Rod- shaped or cylindrical forms. Some are short rods, other are long, the majority have pointed ends, and others have tapered ends. arrangement they can be divided into. 1-Bacilli. Single with no regular pattern. 2-Diplobacilli. Occurring in pairs. 3- Streptobacill. Occurring in chins of different lengths.  C-Spiral-shaped bacteria: It can divided into: Vibriones:- The cells resemble a comma in appearance e.g. Vibrio comma. Spirilla:- Coiled forms exhibiting twists with one or more turns. Both vibrones and spirilla have a rigid wall, i.e. the have constant shapes, They move by flagella. They differ in this respect, from another form of spiral bacteria known as spirochaetes. Fig. (9): Spiral shaped bacteria  Higher bacteria: Other forms of bacteria show resemblance to other groups of microorganisms such as fungi, algae and protozoa. These forms are classified under the higher bacteria which include the Actinomycetes (bacteria resembling fungi) and spirochaetes (bacteria resembling protozoa). 1- Actinomycetes: The actinomycetes form an order of bacteria that resembles fungi in their filamentous branching structure.  Streptomyces, abundant in the soil. Several antibiotic drugs are obtained from species of Streptomyces, streptomycin from S. griseus, chloromycetin from S. venezuelae.. Fig. (10): Actinomycetes (Streptomyces sp.) and Spirochaetes II- Bacterial cell Structure: Fig. (11): A generalized bacterial cell.  II- Bacterial cell Structure: The essential components of a bacterial cell are. Cell wall: Bacterial cell wall is relatively rigid and elastic. It is porous in structure allowing the passage of solutes with molecular weights smaller than I mm in diameter. The composition of the cell wall varies from one bacterial species to other but there is a basal structure in all species. This is composed of a substance called mucopeptide, murein or glycopeptides" to which the strength of the cell wall is owed. The cell wall also contains special components in addition to the basal mucopeptide structure. These special components are generally simple and present in a little amount in gram - positive bacteria, but are complex and large in amount in gram- negative bacteria. The cell wall protects the, delicate, cytoplasm membrane and maintains the characteristic shape of the micro-organism. It also plays an essential role in cell division. 2- The cytoplasmic membrane: This is a thin elastic membrane formed of a double layer of phospholipid. - It is Selective permeability and transport of solutes. - Electron transport and oxidative phosphorylation.. - It contains enzymes that function in the biosynthesis of DNA and cell wall.  3- capsule: The slime layer, surrounds most bacteria and may vary in thickness even in different cells of the same culture. When the material is firm, gelatinous and become more definitive in structure it is called a "capsule" It affords the cell some protection against drying; it may also protect the bacteria from the normal body defenses against invasion. Since we find that the heavily encapsulated pathogenic bacteria are generally more virulent than the strains without capsules. 4- Flagella: Many species of bacteria are motile- many are not. A creeping or gliding type of movement is exhibited by some of the sulfur bacteria. But the mechanism by which this is accomplished is not well understood. The free swimming bacteria have filamentous appendages called "flagella" which are considered to be organs of locomotion. Chemical analysis of isolated flagella shows that it composed of a protein called "flagellin".  5- Cytoplasm: The cytoplasm of bacteria is less highly organized than the cytoplasm of higher plants. It is the internal environment of the cell that contain various kinds of granules like ribosomes, polysaccharide, nuclear material, mesosomes and other materials characteristic of a particular organism. It is considered to be a colloidal system consisting of proteins, fats, carbohydrates, mineral matter and water. 6- Nuclear material Bacterial cells do not contain the nucleus characteristic of the cell of higher plants and animals. They do, however, contain "bodies" within the cytoplasm that are regarded as a nuclear structure which is filled with DNA. DNA is proved to be in the form of one contionus folded thread, it is concluded that the bacterial nucleus is also the bacterial chromosome. It is a closed loop of DNA contains the hereditary information's.  7- The inclusion granules: The bacterial cytoplasm contains a variety of non essential structures which may disappear under certain conditions of growth. In the presence of adequate nutrients, they accumulate in a large number and acts a reservoir for the time of need. For example: Volutin granules and lipid granules.  Endospores Many bacteria produce thick-walled resting cells which are highly resistant to such unfavorable environmental conditions as drought and extremes of heat and cold. Although they may not be really comparable to the spores of other organisms, the resting, cells are, generally called Endospore. Bacterial spores may stand temperatures as low as-260C or as that of boiling water for several hours without losing their power to give rise to normal vegetatively active cells, under suitable environmental conditions the spore germinates either immediately or after a dormancy period. A single spore, and the germination of a spore gives rise to only a single vegetative cell. Spore formation usually occurs in rod-shaped bacteria (Bacillus. and Clostridium). The formed spore may be located either centrally , terminally or subterminally. In some bacteria the spore diameter is greater than the width of the bacterial cell e.g. Cl tetani is swollen, spherical and terminal.