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

Iron(III) reducing bacteria (IRB) are best known and most influential drivers for mobi-lising 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 (S 0 ) 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 S 0 at pH 6.5. The results show that although the extent of Fe(III) reduction ( > 100 μ mol) was over ten times greater than that of S 0 reduction ( < 8 μ mol), it was S 0 reduction that immobilised Sb through Sb 2 S 3 precipitation. Further, the thermodynamic calculation suggests that such great impacts of marginal S 0 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 S 0 reduction over the central Fe(III) reduction.