Give a detailed account of how bacteria are useful for humans.

Following are the uses of the bacteria:

1. Production of butter and cheese — Some bacteria such as Streptococcus and Lactobacillus are used to produce curd, butter and cheese.
2. Production of vitamins — Many bacteria living in the intestine of humans synthesize vitamins such as vitamin B.
3. Production of medicines — Bacteria are also used in the production of certain antibiotics such as streptomycin and aureomycin.
4. Nitrogen fixation — Some bacteria such as Azotobacter and Clostridium live in the root nodules of leguminous plants and fix atmospheric nitrogen into nitrates.
5. Nitrification — Some bacteria such as Nitrosomonas convert ammonia into nitrates and increase the fertility of soil.
6. Curing of tobacco and tea leaves — Bacteria are used in the curing of tobacco and tea leaves. Curing imparts a characteristic flavour to tobacco and tea leaves.
7. Digestion of food — Some bacteria live inside the digestive tract of animals, especially herbivores and break down cellulose (in grass) and help in digestion.
8. Decay of organic waste — Bacteria are the scavengers of nature and help to keep the environment clean. They act on the dead bodies of plants and animals and break them down into simpler chemical compounds. During decomposition, they release carbon, nitrogen and sulphur into the atmosphere