The structure of the Bacterial cell is very simple which can be observed under an electron microscope. The cell shows prokaryotic organization. It has following parts:
(A) Cell Wall:
The protoplasm of the cell is surrounded by a cell wall (rigid, 10—25mm thick). Cell wall is made up of mainly polysaccharides (glucans, mannans, galactans), chitin, muramic acid, and an amino diaminopimelic acid.
This is outside cell wall and formed by slimy polysaccharides, lipids and proteins. It is hard when dry but slimy and gel – like when moist. It is formed by materials secreted from protoplasm. This acts as a protective cover against dryness, high temperature etc. Capsulated bacteria are dangerous since they can survive antibiotic action or phagocytosis action of white blood corpuscles in man.
Internal to the cell wall there is a thin plasma membrane, which is rich in lipids. The protoplast is homogeneous which contains many small vacuoles and incipient nucleus and stored food granules. The granules are of volutin, glycogen, fats and proteins. An organized nucleus with nucleolus and nuclear membrane is absent. The chromatin granules are dispersed in the protoplast in form of one or two deeply staining bodies. The chromatin granules are composed of DNA (Deoxyribonucleic acid). The plastids and chlorophyll are absent, except in some photosynthetic bacteria. In motile forms the bacterium cell is provided with one or more flagella originating from the cytoplasm.
The protoplasm lacks mitochondria, Golgi bodies, centrioles, plastids and endoplasmic reticulum. Ribosomes are present but of smaller, 70S type. Organized chromosomes are not present in some cases. Some mesosome membranes form by imagination of plasma membrane. It is believed that they contain respiratory system enzymes.
The flagella are distributed over the surface of the bacterial cell. On the basis of number and arrangement of flagella, bacteria are classified into the following types:
(A) Monotrichous : Here the bacterial cell bears only a single flagellum at one pole of the cell. Each flagellum has more than two curves, e.g.,Vibrio.
(B) mphitrichous : ln this case, at both the poles or near the posses more than one flagellum are present, e.g., Nitroson.
(C) Lophotrichous : Thtre are more than one flagellum at one pole. The flagellum has one or two curves, e.g., Thiospirillum.
(D) Peritrichous : In this case a large number of flagella are distributed evenly all over the cell surface, e.g., Bacillus typhi. (E) Atrichous—Flagella absent, e.g., Micrococcus.