Effects of phosphate-solubilizing bacteria on phosphorous release and sorption on montmorillonite

Most of P is fixed in pedosphere and lithosphere, i.e., not directly available to ecosystem. Interactions between phosphate-solubilizing bacteria and clay minerals contribute heavily to P biogeochemistry. In this study, hydroxylapatite (HAp), montmorillonite (Mt.) and Enterobacter sp. were applied to investigate their influences on P release, sorption, and transformation. Enterobacter sp. promoted the dissolution of HAp via secreting formic acid (pH declined from neutral to similar to 5.0). However, respiration of the bacteria with addition of Mt. was decreased by similar to 15.0% after their logarithm growth. SEM analysis also indicated that the number of Enterobacter sp. cells was significantly reduced on Mt. surface. Mt. was hence able to inhibit the activity of the adsorbed bacteria on its surface. Meanwhile, the mobile bacteria helped to transform HAp mineral to nanoparticles via partial dissolution. Despite the low sorption of mobile P anions (< 0.2 mg L-1), Mt. was able to adsorb plenty of HAp nanoparticles. The subsequently enhanced adsorption of P nanoparticles by Mt. protects the environment from P losses. Therefore, interaction of mobile bacteria and clay minerals have a positive feedback in regulating P transportation in long-term. This study elucidated the different roles of mobile and fixed bacterial cells in P biogeochemistry influenced by Mt.