Soil organic carbon and phosphorus availability regulate abundance of culturable phosphate-solubilizing bacteria in paddy fields

Low availability of phosphorus (P) is a major constraint for optimal crop production, as P is mostly present in its insoluble form in soil. Therefore, phosphate-solubilizing bacteria (PSB) from paddy field soils of the Indo-Gangetic Plain, India were isolated, and their abundance was attempted to be correlated with the physicochemical characteristics of the soils. Ninety-four PSB were isolated on Pikovskaya's agar medium, and quantitative phosphate solubilization was evaluated using NBRIP medium. The isolates solubilized P up to a concentration of 1 006 μg mL⁻¹ from tricalcium phosphate with the secretion of organic acids. These isolates were identified by 16S rRNA gene sequence comparison, and they belonged to Gammaproteobacteria (56 isolates), Firmicutes (28 isolates), Actinobacteria (8 isolates), and Alphaproteobacteria (2 isolates). Phylogenetic analysis confirmed the identification by clustering the isolates in the clade of the respective reference organisms. The correlation analysis between PSB abundance and physicochemical characteristics revealed that the PSB population increased with increasing levels of soil organic carbon, insoluble P, K⁺, and Mg²⁺. The promising PSB explored in this study can be further evaluated for their biofertilizer potential in the field and for their use as potent bio-inoculants.