(i) Digestion: E. coli and Bacillus help in human digestion.
(ii) Cellulose Digestion: Cattle have a type of bacteria in their intestines. It produces the cellulose digesting enzyme cellulase. Cellulase helps in digestion of hay, grass, leaves, cell walls etc.
(iii) Vitamin production: E. coli and other bacteria in the human intestine produce and supply vitamins B1, B2, K, biotin etc.
(iv) Insulin production: E. coli bacteria are used to produce insulin hormone. It controls diabetes.
(v) Genetic engineering: Agrobacterium tumefaciens and E. coli bacteria are of immense importance in genetic engineering.
(vi) Preparation of dairy food: curd, cheese, butter etc. are made from milk. Bacteria like Streptococcus lactis, Lactobacillus etc. are used to make these foods.
(vii) Probiotic bacteria: About 500 species of bacteria live in the human digestive system as mitotic bacteria. All these bacteria are called probiotic bacteria. Probiotic bacteria help in human digestion. So they are considered as friendly and helpful bacteria of humans.