Elevated heterotrophic activity in Guaymas Basin hydrothermal plumes influences deep-sea carbon cycling.

Deep-sea hydrothermal plumes are characterized by chemoautotrophic production fueled by the oxidation of reduced inorganic substrates. Recently, organic carbon cycling was proposed, but the metabolic fate of organic carbon is unconstrained. Here, we investigate organic carbon metabolisms in and around a hydrothermal plume to constrain the impacts of hydrothermal vents on deep-sea carbon cycling. Acetate and methanol are detected throughout the water column and are rapidly metabolized in Guaymas Basin waters. Heterotrophic production, up to 7.69 µg C L-1 d-1, greatly exceeds chemoautotrophic production. Relative to shallow water, elevated microbial activity coincides with a distinct plume signature, indicating that microbial communities respond quickly to hydrothermal inputs. Metatranscriptomic analysis of functional genes for heterotrophic metabolisms implicates Gammaproteobacteria and diverse heterotrophs in hydrothermally-sourced organic carbon degradation. Our results illustrate that organic carbon is differentially cycled within hydrothermal plumes, suggesting that hydrothermal inputs profoundly impact heterotrophic activity in the deep sea.