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Note on the use of Microbes for
Improving Soil Fertility

Microorganisms play several key roles in the environment. Besides their, well-known activities in biogeochemical cycling, soil fertility maintenance etc., several microbes could be shown very helpful in maintenance of environmental quality through biodegradation of wastes (urban, municipal and industrial) into useful products and also in biodegradation ofharmful pesticides used in crop protection and public health. DOT, lindane heptachlor, chlordane, malathion etc., are biodegraded by several bacteria, and fungi. These microbes are thus efficient purifiers of the environment.

The use of mycorrhizae to enhance the uptake of nutrients and water for establishment of seedlings on degraded lands. This will, however, not lead to the improvement of soil fertility by mycorrhizae as such, although the success of plant growth will eventually lead to reclamation of degraded lands. However, nitrogen fixing bacteria like Rhizobium or actionomycete genus Frankia can be used to induce nodule formation in a variety of plant species, so that these can be used for improving soil fertility of degraded lands. This nodule formation can be induced, both in leguminous and non-leguminous plant species comprising annuals (cereal and legume crops) and perennials (trees). Efforts are underway to manipulate the genes of both host and rhizobia to obtain maximum efficiency of nodule formation. Strains are also being tailored for unusual soil environments representing degraded lands.

Besides this, microbes are also able to remove toxic heavy metals from industrial wastes. Some bacteria are also able to metabolize hydrocarbons in the petroleum and thus very useful in removal of oil-spills and grease from water bodies. A strain of Pseudomonas aeruginosa has been developed in USA which is able to produce a glycolipid emulsifier that reduces the surface tension of an oil- water interface, thus removing oil from water. For removal of grease deposits, a mixture of several bacteria is used.

Some microorganisms can also be used in environmental monitoring and biomonitoring. Environmental pollutants can be detected by the use of appropriate strains of microbes as biosensors. Biosensor is a biophysical device used to detect the presence and quantify the specific substances (sugars, proteins, hormones, pollutants) in the specific environments.

Soil Fertility

Microbes are being exploited in two important ways - biofertilisers, and for creating new nitrogen-fixing organisms.

Biofertilisers Potential of Rhizobium, Azotobacter, Beijerinckia, and Azospirillum, Cyanobacteria, such as species of Aulosira, Anabaena, Nostoc, Plectonema, Scytonema, Tolypothrix, and Azalia as biofertilisers has been exploited so as these could serve as an alternative to chemical fertilizers.

Many brands of rhizobial inoculants are already in market today in the country. Several organization and manufacturers are producing huge quantities of Rhizobium culture in the country. These includes Micro Bac., India, Shyam nagar, Parganas; Bacifil Inoculants, Lucknow; Govt. of TamilNadu; Nitro Fix Industries, Calcutta (W. Bengal) and Indian Organic Chemical Ltd. Bombay. In some other States, units are being prepared for increase in its production. Much progress has also been made with cyanobacteria in this direction. Mycorrhizae, both ecto and endomycorrhiza help in uptake of N, P, K and Ca. They, particularly help in phosphorous nutrition.


Several microbes (viruses bacteria and fungi) are being developed as suitable biopesticides for the management of insect and nematodal pests. Some fungi have good potential of their use as bionematicides to control nematodal pests of vegetables, fruit and cereal crops. Some bacterial and fungal products are also in use to control diseases of roots and shoots of plants.

Nitrogen Fixers

Through recombinant DNA technology efforts have been made to introduce nitrogen-fixing genes (nif genes) into wheat, corn, rice, etc. Plasmids of the bacterium, E. coli and yeast are being worked out for such a possibility. Hybrid E.coli plasmid cloned with nif genes of a nitrogenfixing bacterium, Klebsiella pneumoniae and hybrid yeast plasmids are then integrated.

ENVIS CENTRE Newsletter Vol.6,No 1 March 2008 Back 
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