Abstract:
Phosphorous (P) is considered to be one of the key essential elements demanded by crop
plants. Approximately 70 - 90% of phosphatic fertilizers applied to crops are fixed in soil as
Ca, Fe, and Al metal cations, which are insoluble and thus not readily available for plant
uptake. Therefore, most soils are deficient in plant available P. This is usually rectified by
applying phosphate fertilizers continuously, although this is not economically viable or
environmentally acceptable. The present paper reviews the mechanisms involved with
phosphate solubilization and mineralization by phosphate solubilizing microorganisms
(PSMs) with the associated factors that determine the success. PSMs are effectively involved
in mediating the bioavailability of soil P. Their contribution includes mineralization of
organic P solubilization of inorganic P minerals, and storing sizable amounts of P in biomass
through different mechanisms such as the production of organic and inorganic acids, H2S,
siderophores, exopolysaccharides, and production of enzymes such as phosphatases, phytase,
and phosphonatases/C-P lyases, which are capable of chelating the metal ions, forming
complexes, and making plant available P. PSMs manifest a wide range of metabolic functions
in different environments, resulting in significantly higher plant growth, enhanced soil
properties, and increased biological activities. Therefore, development of bio-inoculants with
efficient novel PSM strains and further investigations on exploring such strains from diverse
ecological niches with multifunctional plant-growth-promoting traits are needed.
