Deep-sea microbes in the global ocean strive under low temperature and high hydrostatic pressure conditions. Microbial activity, however, have been largely measured under atmospheric pressure conditions. In this study, we determined prokaryotic heterotrophic activity under in situ conditions using an In Situ Microbial Incubator (ISMI) and compared the in situ activity with that under atmospheric pressure conditions. The ISMI was deployed from epi- to bathypelagic depths in the Atlantic, Pacific and Southern Ocean. The bulk activity under in situ conditions was increasingly inhibited with increasing hydrostatic pressure. At 4000 m depth, the bulk heterotrophic prokaryotic activity under in situ hydrostatic pressure was about one-third of that measured in the same community under atmospheric conditions. Single-cell analysis showed that about 85% of bathypelagic prokaryotes were piezotolerant, while piezosensitives and piezophiles comprised rather small fractions. Metaproteomics revealed their taxonomically characteristic survival strategies at meso- and bathypelagic depths. Piezosensitive bacteria likely originating from the upper water column increased their activity more than 100-fold upon depressurization. Thus, the higher bulk activity of the deep-sea prokaryotic community measured upon depressurization is due to a small yet highly active fraction of the deep-sea prokaryotic community. Taken together, the heterotrophic prokaryotic activity in the deep-sea is substantially lower than hitherto assumed with major impacts on the carbon budget of the ocean’s interior.

Tutorial/Invited: Invited

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

Authors:

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

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

Eva Sintes, Centre Oceanogràfic de les Balears - Instituto Español de Oceanografía, CSIC  (eva.sintes@ieo.csic.es)

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

Julia Stefanschitz, GEOMAR Helmholtz Centre for Ocean Research Kiel  (jstefanschitz@geomar.de)

Murat Kısadur, University of Vienna  ()

Motoo Utsumi, University of Tsukuba  (utsumi.motoo.ge@u.tsukuba.ac.jp)

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