The economic importance of bacteria are
(a) In agriculture or In soil fertility :
Some bacteria increase soil fertility, Nitrogen is essential for all plants. Nitrogen occupies 80% of the atmosphere. The plants take nitrogen in the form of nitrates. In soil nitrates are formed by three processes:
(i) By nitrogen-fixing bacteria : Bacteria are found in soil either free e.g., Azotobacter and Clostridium or in root nodules of leguminous plants, e.g., Rhizobium leguminosarum. These bacteria are capable of converting atmospheric free nitrogen into nitrogenous compounds.
(ii) Nitrifying bacteria : These bacteria convert nitrogen of ammonia into nitrite (NO2) e.g., Nitrosomonas, and convert nitrite compounds into nitrates e.g., Nitrobacter.
(iii) Decay of dead plants and animals : Some bacteria attack dead bodies of plants and animals and convert their complex compounds into simpler substances, e.g., Carbon dioxide (CO2) water (H2O), nitrate (NO3), sulphate (SO4), etc.
(b) In Dairy :
Bacterium lactici acidi and B. acidi lactici are found in milk. These bacteria ferment lactose sugar found in milk to form lactic acid by which milk becomes sour. If the milk is heated at 62.8°C for 30 minutes and is simultaneously cooled, the number of lactic acid bacteria is reduced but all spores and cells of these bacteria are not destroyed and pathogenic spores are destroyed. In this way milk becomes sour but it takes longer time to become sour than ordinary milk. This process is known as pasteurization.
Lactic acid bacteria bring together droplets of caesin, a protein found in milk and help in the formation of curd.
On churning of curd, butter is derived in the form of fat's rounded droplets. The butter on heating is converted into "ghee".
On freezing of case in of milk protein it is fermented by bacteria with the result that foamy and soft substance, different in taste is formed.
(c) Industrial value :
From industrial point of view bacteria are most important Some of the uses of bacteria in industries are as follows:
(i) Vinegar industry : Vinegar is manufactured from sugar solution in the presence of Acetobacter aceti.
(ii) Alcohol and Acetone : Clostridium acetobutylicum takes part in the manufacture of butyl alcohol and acetone.
(iii) Fibre ratting : By this process fibres of jute, hemp and flax are prepared. In the preparation of flax, hemp and jute, the ratting of stems of Linum usitatissimum (Flax=Hindi Sunn), Cannabis saliva (Hemp=Hindi Patson) and Corchorus capsularis (Jute) respectively is done. In this process the stems are kept under water for some days and when stem begins to decay fibres are separated from the stem on thrashing. The process of separation of fibres is known as ratting. This process is carried out by Clostridium butyricum inhabiting the water.
(iv) In tobacco industry : Bacillus megathenium mycococcus is used for its fermentative capacity for developing flavour and taste in tobacco leaves.