Anaerobic oxidation of short-chain volatile alkanes

The short-chain volatile alkanes ethane, propane, and butane are major components of natural gas. Released from deep-seated subsurface reservoirs through natural seepage or gas extraction, they percolate through anoxic and oxic environments before reaching the atmosphere, where they contribute to tropospheric chemistry and act as greenhouse gases. While their aerobic biological oxidation is well established, their fate in anoxic environments has only recently come into focus. Here we review their oxidation in anoxic settings - from subsurface reservoirs and deep-sea seep sediments to terrestrial hot springs and wastewater treatment plants. We discuss the phylogenetic diversity, biochemical mechanisms, and physiology of microorganisms mediating anaerobic oxidation of volatile alkanes, including nitrate- and sulfate-reducing bacteria (SRB) and the recently discovered alkane-oxidizing archaea. We also highlight advances in diagnostic tools, such as stable isotope analyses and single-cell chemical imaging. Finally, we outline major unresolved research questions, including the unique biochemistry of anaerobes and the extent to which they act as natural biofilters by reducing atmospheric emissions of volatile alkanes.