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

南冰洋，也被称为南大洋，在海洋的生物泵功能中起着至关重要的作用。据推测，南大洋约占全球海洋二氧化碳吸收量的30%，因此对缓冲大气中不断增加的二氧化碳水平至关重要。由光合作用初级生产产生的生物聚合物质的降解调节了海洋中储存的碳量。然而，冷适应细菌快速溶解和分解藻类中复杂多糖的分子和生理机制尚不清楚。我们从南极海域分离出一种嗜冷的海洋γ变形菌，halplankton Pseudoalteromonas ANT/505，它具有广泛的多糖分解能力。这种细菌在南大洋的地表水中大量可检测到，可以通过基因操作进行修改，并且在这里提出作为一种模式生物来揭示决定极地地区多糖转化的嗜冷适应性。本项目旨在阐明该模式菌利用海洋多糖的具体机制。我们将功能表征果胶和海藻酸盐特异性运输和降解途径。我们将通过蛋白质基因组学分析将这些途径与其他盐浮游藻的多糖利用机制进行比较。我们将研究多模块酶如何增加与底物的相互作用，并在稀释的海洋环境中支持多糖降解。最后，细胞外囊泡和附属物对果胶和海藻酸盐特异性多糖降解过程的功能将在低温条件下进行举例研究。这个项目将研究与南大洋碳循环有关的生物过程。该项目的研究结果将有助于更好地了解极地海洋中多糖的分解代谢过程，这是表征气候变化条件下南大洋生物泵功能的先决条件。

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.