Microbial Ethane and Propane Production and Ethanogenic Enrichment of Methanogens in Coastal Sediments

Abstract Ethane and propane are short‐chain alkanes that are ubiquitous in marine environments, while the biological formation of ethane and propane remains largely unconstrained in coastal subsurface sediments. Here, we detected nanomolar concentrations of ethane and propane along 2.7–5.7 m sediment cores with different geochemical gradients at coastal sites of the East China Sea. We further conducted sediment incubation experiments and demonstrated that diethyl sulfide, bromoethane, ethanethiol, ethanol, and acetate were potential precursors for ethane biosynthesis, while propane could be produced from propanol and propanethiol. Ethane production was influenced by the change in temperature, substrate concentration, and H 2 partial pressure. Particularly, the addition of 80% H 2 in the headspace resulted in a 75‐fold increase in ethane production, suggesting the involvement of H 2 in ethanogenesis. The addition of methanogenesis inhibitor, 2‐bromoethanesulfonate, completely terminated the activity of methanogens and also inhibited ethane production. Taxonomic profiling of the ethane‐producing enrichment suggested that methanogens, primarily from the orders Methanomicrobiales , Methanosarcinales , and Methanococcales , might be involved in the formation of trace amounts of ethane, which was probably achieved via the proposed intermediate of CH 3 CH 2 ‐S‐CoM in a similar pathway for methane production. These results reveal the potential role of methanogens in ethane production and provide insights into the biogeochemical cycling of hydrocarbons in coastal sediments.