RT Journal Article SR Electronic T1 Significant organic carbon acquisition by Prochlorococcus in the oceans JF bioRxiv FD Cold Spring Harbor Laboratory SP 2022.01.14.476346 DO 10.1101/2022.01.14.476346 A1 Zhen Wu A1 Dikla Aharonovich A1 Dalit Roth-Rosenberg A1 Osnat Weissberg A1 Tal Luzzatto-Knaan A1 Angela Vogts A1 Luca Zoccarato A1 Falk Eigemann A1 Hans-Peter Grossart A1 Maren Voss A1 Michael J. Follows A1 Daniel Sher YR 2022 UL http://biorxiv.org/content/early/2022/01/15/2022.01.14.476346.abstract AB Marine phytoplankton are responsible for about half of the photosynthesis on Earth. Many are mixotrophs, combining photosynthesis with heterotrophic assimilation of organic carbon but the relative contribution of these two carbon sources is not well quantified. Here, single-cell measurements reveal that Prochlorococcus at the base of the photic zone in the Eastern Mediterranean Sea are obtaining only ~20% of carbon required for growth by photosynthesis. Consistently, laboratory-calibrated evaluations of Prochlorococcus photosynthesis indicate that carbon fixation is systematically too low to support published in situ growth rates in the deep photic layer of the Pacific Ocean. Furthermore, agent-based model simulations show that mixotrophic cells maintain realistic growth rates and populations 10s of meters deeper than obligate photo-autotrophs, deepening the nutricline and Deep Chlorophyll Maximum by ~20 m. Time-series of Prochlorococcus ecotype-abundance from the subtropical North Atlantic and North Pacific suggest that up to 30% of the Prochlorococcus cells live where light intensity is not enough to sustain obligate photo-autotrophic populations during warm, stratified periods. Together, these data and models suggest that mixotrophy underpins the ecological success of a large fraction of the global Prochlorococcus population and its collective genetic diversity.Competing Interest StatementThe authors have declared no competing interest.