Methanotrophic acetogenesis drives a novel pathway of arsenic mobilization in reducing groundwaters

Abstract

Geogenic arsenic (As) contamination in groundwater, widely used as drinking water, poses a global health risk, yet the microbial pathways linking electron donor oxidation to the reduction of As-bearing Fe(III) oxyhydroxides remain poorly understood. Here, we deployed Fe(III) (oxyhydr)oxide-coated pumice stones in high-As, high-methane groundwater in Cambodia for 270 days to capture planktonic metal-reducing microbial communities in-situ. These were used to inoculate anaerobic microcosms with methane or volatile fatty acids (VFAs) as electron donors over 200 days. Genome-resolved metagenomics revealed that methane oxidation via reverse methanogenesis led to acetate production, which in turn provided the primary electrons for Fe(III) and As(V) reduction in the microcosms, resulting in As(III) release. Our findings highlight an indirect coupling between methane oxidation and arsenic mobilization, with acetate as the key intermediate. This study offers new insights into the role of methane in subsurface biogeochemical cycling and its implications for arsenic contamination in groundwater systems. SynopsisThe study uses a novel in situ sampling procedure, coupled with metagenomic analysis, to identify anaerobic methane oxidation producing acetate, as a potentially important pathway to generate electron donors for microbial Fe(III) and As(V) reduction in aquifer sediments. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=72 SRC="FIGDIR/small/696296v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@801222org.highwire.dtl.DTLVardef@268d01org.highwire.dtl.DTLVardef@f342e2org.highwire.dtl.DTLVardef@ac1f9d_HPS_FORMAT_FIGEXP M_FIG C_FIG