Optimization of growth conditions for Azotobacter species and their use as biofertilizer
Biofertilizer is a large population of a specific or a group of beneficial microorganisms for enhancing the productivity of soil either by fixing the atmospheric nitrogen by solubilizing soil phosphorus or by stimulating plant growth through synthesis of growth promoting substances.1 Biofertilizer supply in addition to nitrogen considerable amount of organic matter enriching structure of soil. Inoculants of these microorganisms have proved their technical feasibility, economic viability and social acceptability. Biofertilizers are the most advanced biotechnology invention which is necessary to support developing organic agriculture, sustainable agriculture, green agriculture and non pollution agriculture. The biofertilizer can increase the output and improve the quality of agricultural products.2 Biofertilizers have definite advantage over chemical fertilizers. Chemical fertilizers supply only nitrogen whereas biofertilizers provide in addition to nitrogen certain growth promoting substances like hormones, vitamins, amino acids etc. to the plants.3 Crops have to be provided with chemical fertilizers repeatedly to replenish the loss of nitrogen utilized for crop growth. On the other hand biofertilizers supply nitrogen continuously throughout the entire period of crop growth in field under favorable conditions.4 Biofertilizers are formed by mixing of microorganisms with some carriers like lignite and peat moss in a certain amount. Some of the commonly used biofertilizers are Azotobacter biofertilizers, Phospho biofertilizers, Rhizo biofertilizers and Trichoderma biofertilizers. A large number of soil microorganisms are used as biofertilizer. Some of these are phosphate solubilizing microbes including Pseudomonas striata, Bacillus megaterium and Bacillus subtilis).5,6 Some fungi like Aspergillus and Penicillium are potential solubilizer of bound phosphates.7 Azotobacter is one of the most important microorganisms, which is widely used as biofertilizer (Pereira and Shetty, 1987) Azotobacter is Gram negative and polymorphic bacterium i.e. having different sizes and shapes. Their size ranges from 2 3 umin diameter and of various lengths. Azotobacter spp. are sensitive to acidic pHhigh salts and temperature above 35C.7