Role of growth conditions and physicochemical factors controlling the removal and biomineralization of U(VI) by Stenotrophomonas bentonitica BII-R7.

Microbial U(VI)-phosphate biomineralization-based bioremediation has gained attention as a cost-effective and eco-friendly strategy. However, key environmental and biological factors controlling the process remain unclear. The present work assesses the influence of pH and physiological state of Stenotrophomonas bentonitica BII-R7 cells on U(VI) biomineralization under growing and non-growing conditions. The results showed that biomineralization was more effective at growing cells, removing up to 95 % of soluble U after 24 h, forming needle-shape accumulates on the cell surface and extracellular that avoid the entrance of U(VI) in the cells. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and time-resolved laser-induced fluorescence spectroscopy (TRLFS) analyses, along with the phosphatase activity detected under these conditions, suggested a two-stage process: first, a fast-passive biosorption of U(VI) to organic phosphate groups of the cell surface and secondly the biomineralization in form of U(VI)-phosphate precipitates by the activity of phosphatase enzymes. Furthermore, the pH seemed to influence the efficiency of the biomineralization, being more effective at pH 7 than 5.5, as it could affect the free functional groups available for biosorption. Therefore, the results highlight the key factors that need to be controlled for the long-term removal of U(VI) via biomineralization for bioremediation purposes.