Alkane-oxidizing consortia produce substantial amounts of disaccharides

Consortia of archaea and partner bacteria couple the anaerobic oxidation of alkanes to sulfate reduction. While the catabolic pathways in anaerobic alkane-oxidizing archaea (ANKA) have been extensively studied, their anabolic capacities remain poorly understood. Here, we examined nine enrichment cultures dominated by ANKA and their partner bacteria for small-molecular compounds using solvent extraction and gas chromatographic analysis of derivatized extracts. All alkane-degrading cultures contained substantial amounts of disaccharides in their metabolite pools. Cold-adapted methane-oxidizing cultures dominated by ANME-2c and Seep-SRB2 contained up to 1.5 mg of trehalose per mg soluble protein. Trehalose was also abundant in ethane-oxidizing cultures of Candidatus Ethanoperedens and its distinct partner SRBs, accounting for up to 75% of the extracted metabolites. In contrast, thermophilic ANKA cultures dominated by ANME-1 or Candidatus Syntropharchaeum and Candidatus Desulfofervidus contained an abundant as-yet-unidentified hexose-containing disaccharide. Metagenomic analysis revealed widespread trehalose metabolism genes among partner Desulfobacterota and in ANME-2c and Ca. Ethanoperedens, but lower potential in ANME-1 and Ca. Syntropharchaeum, consistent with metabolite profiles. When exogenous trehalose was added to a thermophilic ethane-oxidizing enrichment, we observed rapid metabolization by heterotrophic microorganisms but poor assimilation by the Ca. Ethanoperedens/Ca. Desulfofervidus core community, indicating that ANKA/SRB consortia do not consume externally supplied trehalose. Instead, Ca. Ethanoperedens/Ca. Desulfofervidus, as well as other ANKA/SRB consortia, may use the disaccharides as energy-storage molecules, osmolytes, or components of the extracellular matrix. The disaccharides produced by the consortia also sustain ancillary heterotrophs, thereby linking alkane oxidation to broader sedimentary carbon cycling.