Subproject B3 – Mechanisms of polysaccharide degradation of particle-associated microbial communities

Responsible: Katharina Riedel, Ernst-Moritz-Arndt University, Greifswald

Marine snow consists of organic particles and particle-associated microbial communities that are embedded in a sugary matrix and plays a central role in carbon cycling. The potential for distinct compositionality and functionality among planktonic marine bacteria has been demonstrated by integrated omics-approaches (Teeling et al., 2012). In contrast, structure and function of particle-associated bacterial communities are still largely unexplored. We hypothesize that different phylogenetic groups are present on the particles. Moreover, we propose, that some planktonic bacterial phyla might also be present in the consortia living on algae or other particles; however, the expression profiles of these particulate bacteria differ significantly from those of their free-living counterparts, as they must adapt to other environmental conditions (i.e. sessile lifestyle). To proof these hypotheses, we combine metagenomics, FISH analysis, and state-of-the-art gel-free metaproteomics to unravel which taxonomic groups are present on marine aggregates, which are the metabolic key-players on these particles, which are the key-functions involved in polysaccharide degradation on the particles, and how composition and expressed functions of particulate bacteria respond to diatom blooms. Here, we apply our established methods concerning particulate organic matter proteomics that we developed on soils, pathogenic biofilms and microbial mats to the study of marine particles and validate the obtained data by complementary approaches (i.e. FISH, in situ activity measurement of selected polysaccharide-degrading enzymes, targeted high-throughput proteomics). In the long term, we will investigate the physiology of key-players isolated from the particles and in depth characterize particle-specific key-functions. Knowledge gained within this subproject will substantially contribute to a better understanding of the ecophysiology of marine particle-associated bacterial communities and will help to elucidate the impact of these bacteria on the marine ecosystem focusing on polysaccharide utilization.