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

可归因于海冰藻类的初级生产量对当前北极海洋生态系统和生物地球化学循环具有季节性和数量上的重要性。虽然光和营养物质作为冰藻产量的决定因素已经被研究了几十年，但冰藻和海冰中其他微生物之间可能促进初级生产力的更复杂的协同效应却知之甚少。对海冰细菌和藻类的研究，包括基因组评估，揭示了被称为相容溶质(CS)的化合物之间的潜在联系，这种化合物通常被微生物用来防止高盐度环境中的渗透休克(细胞爆炸死亡)，以及冰中再生氮的可用性。这项研究将检验季节性协同假说，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卤水中生存，然后随着春季温度变暖、盐度增加和保留CS作为渗透保护剂的必要性减少，然后代谢为碳、氮和能量。细菌转化CS的一个重要最终产物是氨，随着光合作用活性辐射穿透冰层，增加了冰藻在冰内对氮的可获得性。海冰中细菌和藻类之间拟议的季节性协同作用的要素将通过实地和实验室相结合的方法加以检验。海冰卤水将在秋季冻结期和春季水华期间收集，并使用放射性标记和稳定的同位素培养和光谱分析方法，测试细菌对胆碱的吸收、转化为CS和再矿化。后者将揭示导致海冰内基于CS的季节性协同作用的关键细菌种型。温度、盐度、pH、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。现有的和新获得的(基于CS的)海冰细菌的纯培养将通过温度和盐度梯度进行检查，以阐明关键过程。该奖项将有助于启动职业生涯早期极地科学家的教职生涯，并为现场、实验室、计算机和华盛顿州、阿拉斯加和格陵兰的研究生和本科生提供培训机会。通过在格陵兰努克的格陵兰气候研究中心进行拟议的实地研究，这个美国团队将促进来自美国、格陵兰和丹麦的科学家之间的国际合作，为最近结束的国际极地年的成果和持续的泛北极目标增添内容。

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.