SOCLIM_MT. SOCLIM_MT

The availability of dissolved organic matter constrains heterotrophic microbial activity in surface waters of the Southern Ocean, characterized by generally low concentrations of organic carbon. In the region southeast of Kerguelen Island, the island mass effect leads to elevated iron concentration in otherwise HNLC waters. Thus, it represents an attractive site to study locally occurring spring phytoplankton blooms and the response of heterotrophic microorganisms to the release of phytoplankton-derived organic matter. To obtain insight into the types of organic substrates used by the microbial communities, we collected samples at sites with contrasting organic matter supply for metaproteomics analysis during the Southern Ocean and Climate cruise (SOCLIM, Oct 2016). First results indicate the presence of proteins associated with bacterial groups that have previously not been described in the area. Furthermore, differences between the metaproteomes obtained from HNLC waters and iron-replete waters were partially explained by temperature and dissolved organic carbon concentration, as revealed by multivariate constrained ordination analysis. Comparative proteomics of transporter proteins suggest that secondary active tripartite ATP-independent periplasmic transporters (TRAP) are more abundant in HNLC waters, while the ATP-dependent counterparts, TonB-dependent transporters (TBDTs) are relatively more abundant in iron-replete waters. Further analysis on substrate binding proteins will give insight into specific carbon compounds potentially taken up by microbial communities, contributing to our understanding of substrate preferences and organic matter remineralization dynamics in bloom-influenced and non-bloom influenced sites.