Dissimilatory and Cytoplasmic Antimonate Reductions in a Hydrogen-Based Membrane Biofilm Reactor

A hydrogen-based membrane biofilm reactor (H2-MBfR) was operated to investigate the bioreduction of antimonate [Sb­(V)] in terms of Sb­(V) removal, the fate of Sb, and the pathways of reduction metabolism. The MBfR achieved up to 80% Sb­(V) removal and an Sb­(V) removal flux of 0.55 g/m2·day. Sb­(V) was reduced to Sb­(III), which mainly formed Sb2O3 precipitates in the biofilm matrix, although some Sb­(III) was retained intracellularly. High Sb­(V) loading caused stress that deteriorated performance that was not recovered when the high Sb­(V) loading was removed. The biofilm community consisted of DSbRB (dissimilatory Sb-reduction bacteria), SbRB (Sb-resistant bacteria), and DIRB (dissimilatory iron-reducing bacteria). Dissimilatory antimonate reduction, mediated by the respiratory arsenate reductase ArrAB, was the main reduction route, but respiratory reduction coexisted with cytoplasmic Sb­(V)-reduction mediated by arsenate reductase ArsC. Increasing Sb­(V) loading caused stress that led to increases in the expression of arsC gene and intracellular accumulation of Sb­(III). By illuminating the roles of the dissimilatory and cytoplasmic Sb­(V) reduction mechanism in the biofilms of the H2-MBfR, this study reveals that the Sb­(V) loading should be controlled to avoid stress that deteriorates Sb­(V) reduction.