The dark ocean (>200 m depth) is the largest habitat on Earth. Dissolved inorganic carbon (DIC) fixation in the oxygenated waters of the dark ocean is in the same order of magnitude as heterotrophic microbial biomass production. Recent evidence suggests inorganic sulfur oxidation could be a major energy source for deep ocean microbes. However, the global relevance and the identity of the major players in sulfur oxidation in the oxygenated deep-water column remain elusive. In this study we combined single-cell genomics, community metagenomics, metatranscriptomics and single-cell activity measurements. We found that the family classified as UBA868 in the Gammaproteobacteria dominates the total expression of RuBisCO (mainly rcbL type II) genes (average of 34%) and of key sulfur oxidation (soxB and (rdsrA) genes (average of 41% and 71%, respectively) in the global mesopelagic oceanic realm. These organisms were undetectable or at low abundance and activity in surface or bathypelagic layers where other players dominate. Our study also underscores the unrecognized importance of mixotrophic microbes, such as UBA868, in the biogeochemical cycles of the deep ocean.

Primary Presenter: José González, University of La Laguna (jmglezh@ull.edu.es)

Authors:

José González, University of La Laguna, Spain  (jmglezh@ull.edu.es)

Clara Martínez-Pérez, Eidgenossische Technische Hochschule (ETH) Zurich  (martinez@ifu.baug.ethz.ch)

Chie Amano, University of Vienna  (chie.amano@univie.ac.at)

Marion Vial, University of Vienna  (marion.vial@imbrsea.eu)

Semidán Robaina-Estévez, University of La Laguna, Spain  (srobaina@ull.edu.es)

Thomas Reinthaler, University of Vienna  (thomas.reinthaler@univie.ac.at)

Gerhard Herndl, University of Vienna  (gerhard.herndl@univie.ac.at)

Zihao Zhao, University of Vienna  (zihao.zhao@univie.ac.at)

Ramiro Logares, Institute of Marine Sciences (ICM), CSIC, Spain  (ramiro.logares@icm.csic.es)

Sergio Morales, University of Otago, New Zealand  (sergio.morales@otago.ac.nz)

Federico Baltar, University of Vienna  (federico.baltar@univie.ac.at)