The economic importance of bacteria are mentioned below:

Beneficial effects of Bacteria:

1. Role in agriculture

• Nature’s scavengers (ammonifying bacteria): Saprophytic bacteria cause decay and decomposition of dead plants or animals and release the raw-materials for mew generation.Eg, Bacillus mycoides, B. ramosus, and B. vulgaris, etc.

• Nitrifying Bacteria: Nitrifying bacteria (Nitrosomonas and Nitrobacter) convert ammonium compounds into nitrates. It occurs in two steps: In the first step ammonia is oxidized to nitrite by Nitrosomonas and in the second step nitrite is oxidized to nitrate by Nitrobacter.

• Symbiotic nitrogen fixation: Rhizobium, Frankia, etc. live symbiotically in the roots of some plants, fix atmospheric nitrogen, and make it available to plants.

• Manure:Saprophytic bacteria convert farm refuse, dung and other organic waste into manure or compost.

• Ensilage: It is preserved cattle feed or fodder. It is formed by packing fresh chopped fodder sprinkled with molasses.Fermentation activity of bacteria produces lactic acid which has preservative action.

• Gobar gas plant:Bacteria convert animal dung and other organic wastes into manure along with production of fuel gas (methane).

• Sewage disposal: Organic content of sewage is broken down by bacteria.

1. Role in Industry

• Manufacture of organic compounds: Fermentation activities of some saprophytic bacteria are employed in the manufacture of alcohols and acids which are as follows:

Lactobacillus acidus: Lactic acid

Acetobacter aceti: Acetic acid

Clostridium acetobutylicum: Butyl alcohol

Propionic alcohol: Propinobacterium

• Dairies: Lactobacillus is used in souring of milk and producing flavors in butter. The butter and cheese industries entirely depend upon the activities of the lactic acid bacteria. It converts milk protein to curd.

• Vinegar production: Vinegar is a sour-tasting liquid, containing acetic acid. It is prepared by fermenting dilute alcoholic liquid with Acetobacter and Gluconobacter. It is used as a condiment or for pickling.

• Tea and tobacco industries: Mycrococcus candidus is used for curing crude leaves of tea and tobacco. In curing, bacteria eat away the unwanted compounds producing the characteristic flavour to tea, coffee and tobacco.

• Retting of fibre: Stem and leaf fibres of plants are separated from other softer tisues by the action of bacteria, eg: Pseudomonas, Clostridium, etc.

• Curing:Leaves of tea and tobacco,beans of coffee and coca are cured off their bitterness with the help of certain bacteria, eg: Bacillus megatherium.

1. Medical uses

• Production of antibiotics: Number of antibiotics are obtained from mycelial bacteria -Streptomyces.Streptomycin,Chloramphenicol, Tetracyclin, etc are antibacterial antibiotics while a number of antifungal antibiotics are also produced from this bacteria. eg:Hamycin, Trichomycin, Polymyxin, etc. Another bacteria used in production of antibiotics is Bacillus and the antibiotics are Bacitracin, Gramicidin etc.

• Vitamins: Different kinds of vitamins are produced from bacteria as:

Riboflavin from Closridium butylicum

Vitamin B,, from Bacillus megatherium

Vitamin K & B-complex from Escherichia coli.

Negative effects of Bacteria:

1. Pathogenic Bacteria: These bacteria cause great loss to animal and plant life by causing various diseases in them. Some important diseases of humans and plants caused by bacteria are as follows. 

Common bacterial diseases of humans.

Common bacterial diseases of plants:

1. Food spoilage: Many bacteria growing on food-stuff liberate exotoxins and cause food poisoning. The most common food poisoning bacteria is Staphylococcus aureus.

Most of the food materials are excellent media for the growth of bacteria. They grow well when temperature and humidity are favourable. The bacteria change the flavour, smell and appearance of food materials, species of Lactobacillus, Streptococcus, Micrococcus and Proteus are responsible for spoilage of milk and milk products.

1. Bacteria Reduce Soil Fertility: Certain bacteria, e.g. Thiobacillus denitrificans and Micrococcus denitrificans are capable of transforming nitrates to nitrogen which returns to the atmosphere. This process is called denitrification and results in a net loss of soil fertility.