Production of zero valent sulfur from dissimilatory sulfate reduction in a methanogenic bioreactor. Production of zero valent sulfur from dissimilatory sulfate reduction in a methanogenic bioreactor

Dissimilatory sulfate reduction mediated by sulfate-reducing microorganisms (SRMs) has a pivotal role in the sulfur cycle. Recently, zero valent sulfur (ZVS) was demonstrated to be generated from the dissimilatory sulfate reduction, adding in a novel pathway. Nonetheless, the ZVS was only measured from intracellular locations of SRMs, and information on the extracellular ZVS generated from sulfate reduction remains scarce. This study successfully showed the ZVS production from the dissimilatory sulfate reduction both in a bioreactor and batch experiments. The ZVS was produced in the form of polysulfide and largely located at extracellular sites. In the bioreactor, interestingly, ZVS could be generated first from partial sulfide oxidation mediated by sulfide-oxidizing bacteria (e.g., Thiobacillus) and later from the SRMs-driving dissimilatory sulfate reduction when changing the reactor operation from anoxic to methanogenic condition. In batch experiments, increasing the sulfate concentration could improve ZVS production. Based on these results, together with thermodynamic calculations, a scenario was proposed for the ZVS production from dissimilatory sulfate reduction, in which SRMs might utilize sulfate-to-ZVS as an alternative pathway to sulfate-to-sulfide to increase the thermodynamic favorability and alleviates the inhibitive effect of sulfide. This study expands our understanding of the SRMs-mediated dissimilatory sulfate reduction and may have implications in environmental bioremediation.