Brief note on the structures and forms of Bacteria

Structure:

The bacteria are the smallest and the most primitive unicellular organisms. They are mostly unicellular but few form colonies. They are of various shapes and the average size of the organizer is between 0.5 or 2m or even longer.

The form of the bacterium cell is generally constant and typical for each species. Morphologically, the bacteria are of the following types:

Every species of bacteria has a definite form and shape and on this basis of their structure, they are classified as under:

1. Cocci: They are oval or spherical in shape. If they occur singly, they are called as micrococcus; if in pairs – Diplococcus; if in a linear chain streptococcus; and if in clusters like grapes— Staphylococcus.

2. Bacilli: They are usually rod-like, may or may not have flagella. The flagella may be present at one or both the ends or around the entire cell surface. These bacteria may occur singly— bacillus; or may form filaments— Streptobacillus.

3. Vibrio: These bacteria are small and often curved like commas. They are usually motile and have a fiagellum at one end.

4. Spirillum: They are twisted like a screw and have flagella at one end or both the ends.

On the basis of distribution of flagella, bacteria are classified as follows:

1. Atrichous: Flagella are absent.

2. Monotrichous: There is a single flagellum only.

3. Amphitrichous: There are two flagella, one at both the ends of bacterium.

4. Cephalotrichous: There are many flagella that occur at one end only.

5. Lophotrichous: There are many flagella that occur at both the ends of the bacterium.

6. Peritrichous: There are many flagella that occur equally distributed all over the surface of bacterium.