Nitrate promotes the transfer of methane‐derived carbon from the methanotroph Methylobacter sp. to the methylotroph Methylotenera sp. in eutrophic lake water

Eutrophic lakes are major contributors to global aquatic methane emissions. Methanotrophy, performed by methane oxidizing bacteria, results in the production of biomass, fermentation products and/or CO₂, making methane-derived carbon available to non-methanotrophic organisms. Methanotrophs can co-occur with methylotrophs which are expected to consume methane-derived carbon. However, it is unknown if this interaction requires cell-to-cell contact, whether physicochemical factors affect this interaction, and what role this interaction may play in ecosystems and biogeochemical cycling in lakes. Here, we performed incubations of an enrichment culture obtained from a eutrophic lake with ¹³C-labeled methane, revealing the transfer of methane-derived carbon from the methanotroph Methylobacter sp. to a methylotroph of the genus Methylotenera. These microorganisms occurred both in mixed clusters and as single cells, indicating that their interaction does not require physical cell contact. In addition, the carbon transfer between the partners is dependent on the presence of nitrate, which is potentially used by Methylotenera sp. and in turn may affect the methane oxidation rate of Methylobacter sp. This interaction, and its dependence on nitrate, may have important implications for the carbon cycle in eutrophic lakes worldwide.