Collaborative Research: Seasonal Synergy between Bacterial Osmoprotection and Algal Production in Sea Ice

海冰藻类的初级生产量对当前北极海洋生态系统和海洋地球化学循环具有季节性和数量上的重要性。虽然几十年来，人们一直在研究光和营养物质作为冰藻生产的决定因素，但人们对冰藻和海冰上其他微生物居民之间可能促进初级生产的更复杂的协同效应知之甚少。对海冰细菌和藻类的研究，包括基因组评估，揭示了称为相容性溶质（CS）的化合物之间的潜在联系，这种化合物通常被微生物用于在高盐度环境中保护免受渗透压休克（细胞爆炸死亡），以及冰内再生氮的可用性。这项研究将测试一个季节性协同假说，即在秋季冻结期间由冰藻释放的CS前体化合物（如胆碱）被冰中的细菌吸收，转化为CS以在冬季海冰的高盐度盐水中生存，然后随着春季温度变暖，盐度新鲜，以及保留CS作为植物保护剂的需要减少，代谢为碳，氮和能量。这种细菌转化CS的一个重要的最终产物是氨，当光合有效辐射穿透冰时，增加了冰内氮对即将开花的冰藻的可用性。这一拟议的季节性协同作用的元素之间的细菌和藻类包裹在海冰将被检查相结合的现场和实验室的方法。海冰盐水将在秋季冻结和春季开花期间收集，并测试细菌摄取胆碱，转换为CS，和矿化，使用放射性标记和稳定的同位素为基础的孵育和光谱方法。后者将揭示负责海冰内基于CS的季节性协同作用的关键细菌的种类。温度、盐度、pH值、细菌和病毒丰度、叶绿素色素和胞外多糖物质的测量将提供环境和生物背景。将在温度和盐度梯度范围内对现有和新获得的海冰细菌纯培养物（基于CS的培养基）进行检查，以澄清关键过程。该奖项将有助于启动早期职业极地科学家的教师职业生涯，并为研究生和本科生提供培训机会，在该领域，在实验室，在计算机上，以及在华盛顿州，阿拉斯加和格陵兰岛的推广工作。通过在格陵兰岛努克的格陵兰岛气候研究中心进行拟议的实地研究，这个美国团队将促进美国、格陵兰岛和丹麦科学家之间的国际合作，为最近完成的国际极地年的成果和持续的泛北极目标增添新的内容。

The amount of primary production attributable to sea ice algae is seasonally and quantitatively important to current arctic marine ecosystems and biogeochemical cycles. Although light and nutrients have been studied for decades as the determinants of ice-algal production, more complex synergistic effects between ice algae and other microbial residents of sea ice that may foster primary production are poorly known. Studies of sea-ice bacteria and algae, including genomic evaluations, have revealed potential links between compounds called compatible solutes (CS), commonly used by microbes to protect against osmotic shock (death by cell explosion) in high-salinity surroundings, and the availability of regenerated nitrogen within the ice. This research will test a seasonal-synergy hypothesis whereby CS precursor compounds (like choline) that are released by ice algae during fall freeze-up are taken up by bacteria in the ice, converted to CS for survival in the high-salinity brines of winter sea ice, and then metabolized for carbon, nitrogen and energy as spring temperatures warm, salinities freshen, and the need to retain CS as osmoprotectants diminishes. An important end product of this bacterial conversion of CS is ammonia, increasing the within-ice availability of nitrogen to ice algae on the verge of blooming as photosynthetically active radiation penetrates the ice. Elements of this proposed seasonal synergy between bacteria and algae encased in sea ice will be examined by a combination of field and laboratory approaches. Sea-ice brines will be collected during fall freeze-up and spring-bloom periods and tested for bacterial uptake of choline, conversion to CS, and remineralization, using radiolabeled and stable isotope-based incubations and spectroscopic methods. The latter will reveal the key bacterial phylotypes responsible for a CS-based seasonal synergy within sea ice. Measurements of temperature, salinity, pH, bacterial and viral abundances, chlorophyll pigments, and extracellular polysaccharide substances will provide environmental and biological context. Pure cultures of available and newly acquired (on CS- based media) sea-ice bacteria will be examined across temperature and salinity gradients to clarify the key processes.This award will help to launch the faculty career of an early career polar scientist and provide training opportunities to graduate and undergraduate students in the field, in the laboratory, at the computer, and in outreach efforts in Washington State, Alaska and Greenland. By conducting the proposed field research from the Greenland Climate Research Center in Nuuk, Greenland, this US team will foster international cooperation among scientists from the US, Greenland and Denmark, adding to the outcome and continuing pan-Arctic goals of the recently completed International Polar Year.