Conductive Particles Enable Syntrophic Acetate Oxidation between and from Coastal Sediments.

Coastal sediments are rich in conductive particles, possibly affecting microbial processes for which acetate is a central intermediate. In the methanogenic zone, acetate is consumed by methanogens and/or syntrophic acetate-oxidizing (SAO) consortia. SAO consortia live under extreme thermodynamic pressure, and their survival depends on successful partnership. Here, we demonstrate that conductive particles enable the partnership between SAO bacteria (i.e., spp.) and methanogens ( spp.) from the coastal sediments of the Bothnian Bay of the Baltic Sea. Baltic methanogenic sediments were rich in conductive minerals, had an apparent isotopic fractionation characteristic of CO-reductive methanogenesis, and were inhabited by and As long as conductive particles were delivered, and persisted, whereas exclusion of conductive particles led to the extinction of Baltic did not establish a direct electric contact with , necessitating conductive particles as electrical conduits. Within SAO consortia, was an efficient [C]acetate utilizer, accounting for 82% of the assimilation and 27% of the breakdown of acetate. benefits from the association with the methanogen, because in the absence of an electron acceptor it can use as a terminal electron sink. Consequently, inhibition of methanogenesis constrained the SAO activity of as well. A potential benefit for partnering with is that together they competitively exclude acetoclastic methanogens like from an environment rich in conductive particles. Conductive particle-mediated SAO could explain the abundance of acetate oxidizers like in the methanogenic zone of sediments where no electron acceptors other than CO are available. Acetate-oxidizing bacteria are known to thrive in mutualistic consortia in which H or formate is shuttled to a methane-producing partner. Here, we discovered that such bacteria could instead transfer electrons via conductive minerals. Mineral SAO (syntrophic acetate oxidation) could be a vital pathway for CO-reductive methanogenesis in the environment, especially in sediments rich in conductive minerals. Mineral-facilitated SAO is therefore of potential importance for both iron and methane cycles in sediments and soils. Additionally, our observations imply that agricultural runoff or amendments with conductive chars could trigger a significant increase in methane emissions.