In this article we will discuss about the life history of bacillus subtilis.
It is popularly known as Hay bacillus. It is a common example of a rod-shaped bacterium. A rich culture of the bacterium can easily be prepared in the laboratory. Take hay and chop it into small pieces.
Put the chopped bits in water to prepare an infusion. Decant the clear fluid into a flask and plug it with cotton wool. Boil the water in the flask for some time to kill other forms of life except the endospores of hay bacillus which are resistant.
Allow the boiled decoction to cool. The endospores of B. subtilis will germinate on incubation. The decoction will now contain thin films of bacterial cells at the surface of the liquid. They are self-motile. Each cell is furnished with 8-12 flagella.
They are evenly distributed all over the body. The cell has the same structure as described for a typical bacterium cell. It is saprophytic in its mode of nutrition and requires plenty of free oxygen for respiration. The cells secrete slime copiously.
Under normal conditions hay bacillus reproduces by the method of fission. After some time the cells often become attached from end to end after division forming long chains of bacilli sometimes called streptobacilli.
The filaments are embedded in a mass of mucilage which forms a scum on the surface of water. It is the resting or zoogloea stage of the bacterium (Fig. 18.16). B. subtilis being motile, the chains of cells swim.
Being aerobic the chains of cells have avidity for oxygen and thus grow in the scum at the surface of the fluid medium. During the zoogloea stage hay bacillus forms endospores in the same manner as described for the typical bacterium.
The endospores are highly resistant to adverse conditions of life. With the return of favourable conditions the endospores germinate. Each gives rise to a new bacterium cell. B. subtilis is important as a source of antibiotic, subtelin.
