Study On Mechanism Of Interaction Between Bacillus Cereus 12-2 And U(?)

Human industrial activities have led to toxic dissolved uranium into the earth surface environment.It is of great importance to understand the interaction between aerobic or facultative bacteria and uranium in the surface environment,not only for realizing uranium pollution control but also for understanding the new uranium biogeochemical cycle brought by human industrial activities.Current studies reveal that the biomineralization of U?VI?via anaerobes normally produces nano-size U?IV?minerals that can easily re-migrate/re-oxidize,while the biomineralization of U?VI?by aerobes has been constrained because the general mechanism has not yet been fully characterized.In this work,the biomineralization mechanism of U?VI?by B.cereus 12-2?a kind of widely existed facultative aerobes?was investigated.Biosorption experiments revealed that the maximum biosorption capability of intact cells could reach 448.68 mg U/g biomass?dry weight?at pH=5,while a decrease over 60%was induced when the surface carboxyl,amino,and phosphate groups were shielded respectively,especially in the case of carboxyl groups.XRD,SEM and TEM analysis together with tracing the concentration of the soluble uranium within the cell demonstrated that amorphous uranium particles adsorbed extracellularly can directly migrate into cells as solid,and uramphite??NH₄??UO₂?PO₄·3H₂O?with diameter over 10 nm was formed subsequently.The time required for adsorption equilibrium and mineralization by B.cereus 12-2 was shorter when the initial U?VI?concentration was lower within a certain range.Our study also revealed that the biosorption capability was not affected by a high uranium concentration,while the biomineralization process could be inhibited,suggesting that a high concentration of heavy metals may inhibit the activity of enzymes involved in biomineralization process.In addition,it was found that U?VI?could trigger the overexpression of proteins with a molecular weight of22 kD.Proteins of this band were identified by LC-MS,the results showed that this overexpressed band including various phosphatases,kinases and other kinds of enzymes that are related to metabolic process and stimulus response,which may contribute to the intracellular transformation of U?VI?compounds from amorphous phase containing carboxyl groups into crystalline phase containing phosphate groups.Taken together,the immobilization of U?VI?by B.cereus 12-2 contains two major steps:?1?the fast immobilization of U?VI?on the cell surface as amorphous compounds,in which the carboxyl group served as the predominant coordination functional groups and?2?the transport of amorphous particles into cells directly and the enzyme-related formation of uramphite nano-crystals.The immobilization of U?VI?as mineral over 10 nm inside the micrometer cell indicated that B.cereus 12-2 could be potentially applied to treat U?VI?pollutant in aerobic situation for decreasing its mobility.