A mixed consortium of methanotrophic archaea and bacteria boosts methane-dependent selenate reduction

Ling-Dong Shi^a,b, Pan-Long Lv^a,b, Min Wang^a, Chun-Yu Lai^a, He-Ping Zhao^a,b

MOE Key Lab of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Science, Zhejiang University, Hangzhou 310058, China

Abstract

Though methane-based selenate reduction has been reported, neither the selenate load nor the removal rate could satisfy practical applications, thus limiting this technique to bio-remediate selenate pollution. In the present study, using a membrane biofilm batch reactor (MBBR), we successfully enriched a consortium performing methane-dependent selenate reduction, with enhanced reduction rates from 16.1 to 28.9 µM-day^-1 under a comparable Se concentration to industrial wastewaters (i.e., ~500 µM). During active reduction, 16S rRNA gene copies of Archaea and Bacteria were both increased more than one order of magnitude. Clone library construction and high-throughput sequencing indicated that Methanosarcina and Methylocystis were the only methane-oxidizing microorganisms. The presence of 20 mM bromoethanesulphonate or 0.15 mM acetylene both significantly, but not completely, inhibited methane-dependent selenate reduction, indicating the concurrent contributions of methanotrophic archaea and bacteria. Fluorescence in situ hybridization (FISH) revealed that archaea directly adhered to the surface of the membrane while bacteria were in the outer layer, together forming the mature biofilm. This study highlights the crucial role of both methanotrophic archaea and bacteria in methane-dependent selenate reduction, and lays foundations in applying methane to bio-remediate practical selenate pollution.

Graphical abstract

Keywords : Methane oxidation, Selenate reduction, Membrane biofilm batch reactor, Mixed consortium, Wastewater treatment.