PHOSPHATE SOLUBILIZING BACTERIA IN AGRICULTURE BIOTECHNOLOGY: DIVERSITY, MECHANISM AND THEIR ROLE IN PLANT GROWTH AND CROP YIELD.

Phosphorus (P) is an important nutrient second only after nitrogen for plant growth and development.Its adequate amount is present in the soil but nonutilizable by the plants because it is complexed with inorganic metal ions or organic compounds.On an average in different soils its amount varies between 400-1200 mg kg -1 .To overcome the P nutrition requirement farmers use chemical fertilizers which are again ineffective due to the precipitation of a larger proportion of soluble P and also it raises the question of environmental consideration.In such situation, phosphate solubilizing bacteria (PSB) can bring out locked P into plant assimilable form in an ecofriendly fashion.PSB solubilize inorganic P primarily with the secretion of organic acids while organic P is mineralized by secreted phosphatases and phytase enzymes.Several PSB have been isolated, characterized and identified.Among these, the most powerful strains were denominated from the genus Bacillus, Enterobacter, Pantoea, Pseudomonas, Acinetobacter, Rhizobium and Serratia.However, the performance of such isolates is dependent on the soil physicochemical properties and climatic factors.Therefore, it is desirable to isolate, identify and characterize the efficient PSB in relation to soil physicochemical and environmental conditions for the development of soil specific bio-inoculants.Now a day's recombinant biotechnology is seen as a solution for any problem, only the major goal is the identification and isolation of a concerned gene.Thus, the best P solubilizing genes/ consortium of genes may be screened and stably incorporated into the genome of indigenous plant growth promoting bacteria which were adapted to a specific soil and climatic characteristic Copy Right, IJAR, 2016,.All rights reserved. Introduction:-Phosphorus (P) is an essential macronutrient for plant growth and development.It accounts 0.2% of plant dry weight, limits the growth of plants and crop yield (Lin et al., 2006;Sharma et al., 2013).It is required for various metabolic processes, for example-synthesis of biomolecules, energy transfer reactions, photosynthesis, cell division, nutrient uptake, signaling and enzyme activity regulation by phosphorylation of serine, histidine, aspartate, threonine, or tyrosine residues (Raghothama, 1999).Due to integral component all the organisms have developed mechanisms for its assimilation from the environment.Plants absorb P as phosphate anions (HPO 4 --or H 2 PO 4 -) from soil (Rodríguez and Fraga, 1999).However, these phosphate anions are highly reactive in the soil and their precipitation is soil pH dependent.In acidic soils phosphate anions get precipitated with free oxides and hydroxides of aluminium and iron, while in alkaline soils calcium is the main element involved in P fixation (Igual et al., 2001).Thus most soils are deficient in P availability worldwide and especially it is the limiting factor for plant growth and crop productivity in the tropical and subtropical regions (Raghothama, 1999;Richardson, 2001;Schneider et al., 2010).To overcome P limitation, farmers over use chemical fertilizers.P fertilizers are expensive and in developing