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

点击翻译按钮获取中文摘要

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.