The biomineralization process of Ochrobactrum EEELCW01 and its implication for arsenic immobilization

Some bacterial strains have mineralization functions and can effectively reduce the bioavailability of toxic metal(loid) arsenic (As) in soils, but the potential mechanisms are still unclear. In this study, the nitrate-dependent Fe-oxidizing bacterium Ochrobactrum EEELCW01 was used to study the biomineralization process and its extracellular polymeric substances (EPS). In the biomineralization mediated by Ochrobactrum EEELCW01, the products are mainly amorphous Fe oxides and smaller amounts of poorly crystalline goethite. Confocal laser scanning microscopy images confirmed the presence of large amounts of EPS in the bacterial treatments. In the Fe-oxidizing bacteria-EPS-mineral aggregates, exopolysaccharide, Fe(III) and minerals showed a high degree of colocalization. During biomineralization, minerals undergo dissolution-recrystallization cycles, with goethite and siderite as the final stable compounds. Moreover, within 30 days, Ochrobactrum EEELCW01 reduced the soil available As concentration significantly. Our results enhance the mechanistic understanding of the biomineralization and related As immobilization processes mediated by Ochrobactrum EEELCW01, with potential application to the remediation of As-polluted soils.