Methane Oxidation Coupled to Selenate Reduction in a Membrane Bioreactor under Oxygen-Limiting Conditions

Methane-Driven Perchlorate Reduction by a Microbial Consortium

“…In contrast, no methane consumption was detected in batch B without oxygen (Figure b), indicating the essential role of oxygen in methane oxidation. This result is consistent with previous methane-, ethane-, or propane-driven bioremediation studies, in which limited oxygen supply is generally required to activate these gaseous alkanes to drive selenate or nitrate reduction. ,, In addition, oxygen in the headspace remained stable during batch C under methane-absent conditions (Figure c), further suggesting that oxygen consumption was dependent on methane availability. Moreover, the perchlorate reduction rate in batch A (Figure d) was significantly higher than that in batch B ( p < 0.01) and batch C ( p < 0.001), indicating that perchlorate reduction in our bioreactor was predominately driven by aerobic methane oxidation.…”

“…Nevertheless, the proposed microbial mechanisms responsible for methane-supported perchlorate reduction under oxygen-limiting conditions are further proven by a pure culture test of model strains, in which aerobic methanotroph LW13 was unable to reduce perchlorate whereas acetate generated by LW13 was utilized by heterotrophic PRB CKB to complete perchlorate reduction. Similar observations have also been reported in recent studies, in which heterotrophs obtain carbon and energy from methanotrophs-mediated methane conversion to organic metabolites and then reduce selenate. , In fact, acetate as a synergistic link between aerobic methanotrophs and heterotrophic bacteria has been proposed in multiple methane-based MBfR studies. VFAs (predominated by acetate) generated by methanotrophs were hypothesized to support diverse heterotrophic bacteria to reduce various oxidized contaminants including nitrate, ,, bromate, selenate, and perchlorate. , This indicates that synergetic interaction between methanotrophs and heterotrophic bacteria using acetate as an intermediate is likely a universal microbial mechanism for methane-based bioremediation of oxyanions, which requires confirmation in future studies.…”

“…The 12 C-DNA and 13 C-DNA were separated by density gradient centrifugation and fractionation as described previously . Briefly, DNA was mixed with gradient buffer (0.1 M Tris-HCl [pH = 8.0], 0.1 M KCl, and 1 mM EDTA) and cesium chloride (CsCl) solution and then centrifuged at 177,000 g for 48 h at 20 °C using an ultracentrifuge (Optima L-XP, Beckman Coulter, Brea, CA, USA).…”

“…To enrich microorganisms able to couple methane oxidation to perchlorate reduction under oxygen-limiting conditions, a methane-based MBR system similar to our previous study was set up (Figure S1). Briefly, the MBR consisted of two parts.…”

“…Perchlorate stock solution was manually dosed to reach an initial concentration of 0.56 mmol-Cl/L. The operation of incubations was as described previously . Briefly, the incubations were conducted in a 24 h cycle mode and repeated three times.…”