(i) Bacteria are very important for humans. They causes decay and decomposition of dead bodies of plants and animals, so they help in cleaning the earth.
(ii) They fix atmospheric N2 into nitrates, lactic acid bacteria convert milk sugar lactose into lactic acid.
(iii) They convert ethyl alcohol into vinegar, produces butyl alcohol and acetone.
(iv) A number of antibiotics are obtained from mycelial bacterium like streptomycin from Streptomyces bacterium.
