Phosphate Solubilization Mechanisms in Alkaliphilic Bacterium Bacillus marisflavi FA7

This study reports the mechanisms of phosphate solubilization present in alkaliphilic Bacillus marisflavi FA7. The strain obtained from sediment samples of mangrove ecosystem exhibited different mechanisms to solubilize inorganic phosphate and mineralize organic phosphate under alkaline conditions. It reduced the pH of the medium that showed near perfect correlation with tri-calcium phosphate solubilization. Organic acids produced by the strain were detected in broth. Maximum decrease in pH of the medium was observed with NH₄Cl as an inorganic nitrogen source. This indicated involvement of proton extrusion mechanism toward phosphate solubilization during ammonium uptake. It produced exopolysaccharide, but failed to produce siderophore. Bacillus marisflavi FA7 produced extracellular alkaline phosphatase having molecular weight of 175–200 kDa. The pH optimum for maximum enzyme activity was 10.1 and K_m of 1.13 μM p-nitrophenolphosphate. This is the first study to report the highest tri-calcium phosphate solubilization by an alkaliphilic bacterium.