Thermophilic anaerobic ethane oxidation coupled with selenate and selenite reduction

Anaerobic microorganisms are critical in regulating ethane in geothermal environments, where selenate and selenite are common contaminants. Although coupling ethane oxidation with selenate reduction has been demonstrated as feasible, such processes remain poorly explored in geothermal environments. This study addressed this gap by successfully enriching thermophilic anaerobic cultures capable of coupling ethane oxidation with selenate/selenite reduction, achieving selenate and selenite removal rate of 2.7 mg Se/L/d and 2.1 mg Se/L/d, respectively. Metagenomic analysis revealed a novel genus 'Candidatus Ethanivorans selenatireducens', which accounted for 16.0 % and 32.6 % of microbial communities in selenate- and selenite-dependent systems, respectively. This microorganism encoded pathways for anaerobic ethane oxidation via fumarate addition and genes required for the sequential reduction of selenate to elemental selenium. These findings unveiled a novel microbial mechanism linking ethane oxidation and selenate reduction in geothermal systems, providing new insights into the biogeochemical interaction between carbon and selenium in thermophilic environments.