Polysaccharide utilization mechanisms under permanent low-temperature conditions in the Southern Ocean

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The Antarctic Ocean, also known as the Southern Ocean, plays a critical role in the biological pump function of the oceans. It is assumed that the Southern Ocean accounts for about 30% of global ocean uptake of CO2 and is thus crucial for buffering of increasing CO2 levels in the atmosphere. The degradation of biopolymeric material produced by photosynthetic primary production regulates how much carbon is stored in the oceans. However, the molecular and physiological mechanisms that allow cold-adapted bacteria to rapidly dissolve and catabolize complex polysaccharides from algae remain unknown. We have isolated a psychrophilic marine Gammaproteobacterium, Pseudoalteromonas halplanktis ANT/505, from Antarctic waters, which shows a broad capacity to catabolize polysaccharides. This bacterium, which is abundantly detectable in the surface water of the Southern Ocean, is amendable to genetic manipulation and is proposed here as a model organism to reveal psychrophilic adaptations that determine polysaccharide turnover in Polar Regions. The project aims to elucidate specific mechanisms of marine polysaccharide utilization of this model bacterium. We will functionally characterize pectin- and alginate-specific transport and degradation pathways. We will compare these pathways with other polysaccharide utilization mechanisms of P. haloplanktis by proteogenomic analyses. We will investigate how multi-modular enzymes enable an increased interaction with the substrate and support polysaccharide degradation in a dilute marine environment. Finally, the function of extracellular vesicles and appendages for pectin- and alginate-specific polysaccharide degradation processes will be exemplarily investigated under low-temperature conditions. This project will investigate biological processes, which are relevant for the carbon cycle in the Southern Ocean. The results of this project will enable a better understanding of polysaccharide catabolism processes in the polar sea, which is a prerequisite for the characterization of the biological pump function of the Southern Ocean under climate changing conditions.