Phosphate Solubilizing Bacteria for Soil Sustainability

One of the reasons behind the limiting crop yield among industrializing countries at global level is soil infertility. This problem basically originates from the excessive use of chemical fertilizers to meet the ever increasing world food demand. The use of chemical fertilizers has lead to drastic damages to the soil. These include death of useful insects and microorganisms following eutrophication as well as accumulation of potentially toxic elements like arsenic, selenium polluting our underground water resources. All these end up with a depletion of soil fertility. In view of this, the researchers are searching for other dependable sources with a potential to replace synthetic chemical fertilizers. Our soils have three core components; the organic, mineral, and the microorganisms. Out of these, the microorganisms are investigated as biofertilizers to integrate the nutrients in the biological system for an improvement of soil fertility. Among the microorganisms, the phosphate solubilizing bacteria (PSB) have been studied at length for their role in improving plant growth following their application to the crops. PSBs are a diverse bacterial group which help in the plant growth by supplementing the plants with fixed nutrients that are already available in the soil such as phosphorous. These organisms use a mechanism of increasing the growth-promoting hormone, auxin, which directly impacts the growth of plants. Moreover, they also employ the following three mechanisms to improve soil fertility; chelation, lowering pH of soil, and mineralization. Out of the heterogeneous PSB group, the following strains are reported for improving the fertility of soil; Pseudomonas, Bacillus, and Rhizobium. These notable strains have convincingly improved the development, growth, and productivity of crops by mobilizing the amount of inorganic phosphate in the soil increasing its bioavailability for plants without polluting our environment. In the light of these observations the researchers are strongly recommending the use of PSBs as a reliable source for improving soil fertility and ultimately for sustainable agriculture. This chapter reviews the latest developments in this connection.