Q.4. Describe in brief structure of Bacteria.
Related Questions -
Q. Draw neat and labelled sketch of microscopic of bacterial cell. (2013)
Ans. “Bacteria are simplest, unicellular, minute and microscopic organisms grouped under class “ Schizomycetes”. They are cosmopolitan in distribution and occur almost everywhere i.e., in soil, water, plant, animals bodies, air and are resistant to quite higher and lower temperatures.
Morphology or structure of bacteria: -
The existence of bacteria was discovered by Antony Von Leeuwenhoek in 1665. The unit of bacterial life is a cell.
1. Shape of Bacteria: -
Individual bacterial bodies have three basic shape which are— (1) Spherical or ovoid known as coccus (cocci Plural) (ii) cylindrical or rod shaped known as Bacillus ( Baccilli Plural and (iii) curved rod or short spiral known as Spirillum
Cocci: - The word coccus comes from a Greek word Kobbos meaning a globular body and all the cocci have spherical forms there are many species of cocci and they are widely distributed.
Bacilli: - The word bacillus in Latin and means a little stick or rod. These bacteria have shape of a little rod or cylinder. Most of them are straight, rigid rods but some may be slightly curved. Many species are motile, moving by flagella and some are non - motile. Bacili also have many species and are widely distributed.
Spirial: - Spirilipum comes from a Greek word speria meaning a coli. The bacteria have a helicoidal shapes like a crook screw, Some spirilla may be short comma shaped organisms and have less than one complete spirilla turn and known as vibrio.
A forth type of form may occur in few species which in a thread (filament) from e.g. Beggiatoa.
Cell groupings — Among the cocci and to a lesser extents among bacilla, spirilla, the actively growing cells tend to arrange them in some distinct groups.
Fig. - Various Shape of bacteria
Cell groupings in cocci—Cocci usually get arranged in groups of two or more cells and according to number and their made of arrangement they may be known as:
1. Micrococcus: - Coccus cell occurring singly.
2. Diplococi: - Cocci in pairs and usually the adjacents side of paired cells are flattened. ‘The bacteria causing pneumonia gonorhea have this form.
3. Streptococi: - Cocci get arranged in chains due to constant multiplication of cells. The length of chain is variable depending upto species and environment.
4. Staphylococci: - This type of cocci occur in irregular masses resembling more less to clusters of grapes. There cocci divide in more than one plain of space and remain closely adherforming irregulary shaped amuses.
5. Tetrads: - These cocci divide in two planes at right angles to each other forming group of four. The only species of bacteria showing the tetrad arrangement known as Goffkya tertagena (Micrococcus tetrogenus).
6. Sarcinae: - In this form the cocci are in cubical packetx. Sarcina lutea as a harmless species of this class. These bacteria usually found in dust.
Structure of Bacterial cell or Bacterial anatomy: -
Bacterial cell include (a) cell wall and (b) cytoplasm. The cytoplasm is surrounded by a cytoplasmic membrane just inside the cell wall, contains various granules and other cell inclusion and finally athe nuclear material of vital importance. The bacterium also may be enclosed in an envelope or sheath of slime, viscous material forming a more less definite capsule. At the surface of bacterium there may be flagella (organs of locomotion) and some bacilli have pili.
scale of occular
micrometer
MICROBE OR BACTERIA
Fig. A bacterial cell.
(A) Cell wall and cell membrane: -
A bacterial cell usually remain surrounded by three membranes : (a) cytoplasmic membrane—the inner most (b) cell wall—the middle one and (c) Slime layer—the outer most
Slime layer: - It is the modified outer cell wall of bacteria. Sometimes this slime layer is thick and fixed round the cell wall and then termed as capsule. Slime layer gummy and mucilageneous envelopes. Chemically these are found to be polysacharides along with some nitrogenous substances. These bacterial capsules act as a protective material in addition to the cell wall.
Cell wall: - It is rigid, elastic and mainly protective in function the cell wall also
act as selectively permeable membrane. Chemical composition of cell wall is not fully known. The chief chemical constituents of bacterial cell are polysaccharides, oligosaccharides, glucominopeptides, protein lipids, teichoic acids lipoprotein etc.
Gram stain: - It is one of man differential stains for bacteria which serve to divide bacteria into gram positive and gram negative. Imino acid make up in the cell walls of gram positive and gram negative bacteria differ consequently, but it is not well understood wheather this difference is responsible for the differences in the staining reactions of the two groups.
Cytoplasmic membrane: - It is the protein of cytoplasm lying surrounded by Cell wall. It is somewhat thicker and denser than cytoplasm. It consists of huge quantities of lipids and lipoproteins. Its functions is to act as selectivly permeable membrane. Because of its complex nature the chemical structure of the cytoplasmic membrane is not defined.
(B) Cytoplasm: -
The cytoplasm occupies the volume of the bacterial cell surrounded by cell wall and membrane. This bacterial cytoplasm in young stage remain packed with tiny, dense particle which have a strong affinity for staining. These particles are the ribosome as revealed by electron microscope. Ribosomes contain ribonuclic acid (RNA) and proteins. They distributed uniformly in cytoplasm.
Fig. Electron microscopic structure of bacterial cell
In bacterial cultures, the homogeneity of the cytoplasm is usually lost. The formation and separation of some granules or droplets of various substances are known as cell inclusions. Some important cell inclusions are:
(i) Metachromatic granules: - These granules may be observed in bacterial cell by treating them with basic dyes such as methylene blue. They may be found either throughout the cell or massed at the ends of cells. These are actually reserve nitrogenous food substances. Sometimes these granules also referred as past nuclei or as reproductive bodies. These granules are also referred as volution granules.
(ii) Fats (lipid) droplets: - These are usually conciuous in these nitrogen fixing soil bacteria (Azotobactor or Rhizobium) in large free living spirilla, in various acid test bacilli, etc.
(iii) Mesosomes: - This is a membranous structure of cytoplasm and arise a invagination of plasma membrane. The function of these is a matter of conjectie These are active in cell wall synthesis and secretion of extra cellular substance.
(C) Nuclear Structure: - At present evidences concluded that bacterial cell have a nucleus although it is of primitive type.
Recently, with electron microscopic and improved staining techniques some bacteriologist have observed the presence of some granules known as “chromatin granules” and other internal changes in bacteria which indicates the presence and activities of nuclear structures. Chromatin bodies are in reality nucleus have been found in regular numbers during stages of active growth and have been shown to divide just before the whole bacterial cell divides. Chemically the nuclei contain deoxyribo nucleic acid (DNA) probably to a basic protein. The bacterial nuclei is arranged into bundles of fibres and are not remain surrounded by a nuclear membrane . The bacterial nuclei do not undergo mitosis and their mode of replication during division is not known.