A newly isolated indigenous metal-reducing bacterium induced Fe and Mn oxides synergy for enhanced in situ As(III/V) immobilization in groundwater

•Reducing bacteria FMR enhanced in situ As fixation in groundwater by Fe-Mn oxides.•Mn oxide components prevented the bio-desorption of adsorbed As on Fe-Mn oxides.•Bio-reduction of Mn(III/IV) in Fe-Mn oxides created more fresh sites for As adsorption.•Biological passivation of the Mn component inhibited As oxidation but not As fixation.•Bacteria-induced synergy between Fe and Mn oxides promoted the fixation of As(III/V).