Multi-omic insights into chemoautotrophic carbon fixation in deep Antarctic water masses

The Ross Sea (Antarctica) hosts the process of formation and export of two important water masses: High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW). Along the continental slope they mix with Circumpolar Deep Water (CDW) to produce Antarctic Bottom Water (AABW), ultimately affecting the global circulation. In these waters,8 chemoautotrophic archaea and bacteria actively participate in CO2 sequestration, playing a key role in the global carbon cycle. To explore potential chemoautotrophic pathways within the prokaryotic communities in the different water masses we used a multi-omic approach, including metabarcoding and metagenomic analysis, by examining the abundance of key genes involved in inorganic carbon fixation and energy-generating metabolic pathways related to the oxidation of nitrogen, sulfur and methane compounds. Our data show that microbial communities in these water masses potentially utilize four autotrophic CO2 assimilation pathways: the CalvinBenson-Bassham cycle (CBB), the 3-hydroxypropionate cycle (3HP), the dicarboxylate-hydroxybutyrate cycle (DC/4HB) and the reverse tricarboxylic acid (rTCA). Production of new organic carbon is likely driven by ammonia-oxidizing archaea, (e.g. Candidatus Nitrosopumilus) in HSSW and ISW, and by sulfur-oxidizing bacteria (e.g. SAR324 and SUP05) across all water masses.