Padaki, V. G.; Mayali, X.; Weber, P.; Giovannoni, S.; Abraham, K.; Jacobs, K.; Halsey, K.

Labile dissolved organic carbon (LDOC) in the oceans accounts for ~ one fourth of global photosynthesis and turns over with a half-life of about one day, fueling one of the largest engines of microbial heterotrophic production on the planet. Volatile organic compounds (VOCs) are poorly constrained components of LDOC. We detected 78 VOCs totaling 18.5 uM in cultures of the model diatom Phaeodactylum tricornutum, including hydrocarbons usually found in petroleum. In five individual cocultures with bacteria adapted to grow with this diatom, 1 to 66 VOCs were depleted. Two of the most active VOC consumers, Marinobacter and Roseibium, had more VOC oxidation genes, and attached to the diatom, suggesting VOC specialism. Diatom photosynthesis increased by up to 29% in the presence of VOC consumers, indicating that VOC consumption by heterotrophic bacteria in the phycosphere, a region of rapid organic carbon oxidation that surrounds phytoplankton cells, could impact global rates of primary production.