Iron(III) reducing bacteria immobilise antimonite by respiring elemental sulfur

Abstract

Iron(III) reducing bacteria (IRB) are best known and most influential drivers for mobilising metal(loid)s via reductive dissolution of iron(III)-containing minerals. Our study challenges this preconception and found that IRB immobilise metal(loid)s by respiring elemental sulfur (S0) even when Fe(III) reduction is prevailing under mildly acidic conditions. Antimony (Sb), a toxic contaminant, was chosen as an example of metal(loid)s. Antimonite-adsorbed goethite was incubated with Shewanella oneidensis MR-1, a widely distributed IRB, in the presence of S0 at pH 6.5. The results show that although the extent of Fe(III) reduction (>100 μmol) was over ten times greater than that of S0 reduction (<8 μmol), it was S0 reduction that immobilised Sb through Sb2S3 precipitation. Further, the thermodynamic calculation suggests that such great impacts of marginal S0 reduction can be extended to other metal(loid)s via the formation of soluble thio-species or sulfide precipitates. This study redefines the role of IRB in the environmental fate of metal(loid)s, highlighting the strong impacts from the marginal S0 reduction over the central Fe(III) reduction.