Diversity, Vertical Distribution, and Metabolic Activities of Inorganic Sulfur-Cycling Prokaryotes in Lake Fryxell, Antarctica

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Cold environments comprise more than ninety percent of the earth's biosphere yet relatively little is known about the diversity, physiology, phylogeny, and metabolic activities of cold-loving (psychrophilic) microorganisms. This research focuses on bacteria involved in the sulfur. The study is Lake Fryxell, a meromictic lake that contains significant levels of sulfide in the water column. The research will take a polyphasic approach that includes in situ biodiversity studies, isolation and laboratory culture, and molecular analysis of metabolic activity. Each of these objectives will be pursued using a combination of traditional research strategies coupled with novel experimental techniques, the prime objective being to dissect the microbiology and microbial ecology of sulfur-cycling that occurs at 0 degree C in Lake Fryxell. Work will focus on Proteobacteria with the biodiversity studies using metabolic genes rather than ribosomal RNA genes as molecular targets. Targeted genes include pufM, csoS1, and dsr. Isolation and culture of key representatives of each major group of sulfur-cycling prokaryotes will be pursued using a combination of methods, including extincting dilution, high-throughput microtiter plate, and archaeal-targeted enrichments. Molecular measurements of metabolic activity in situ will be combined with these biodiversity and laboratory culture results. Collectively, the results of the proposed research will: (1) reveal for the first time the biodiversity of sulfur-cycling prokaryotes active in an important nutrient cycle at permanently cold temperatures; (2) make available new genetic resources of psychrophilic phototrophs, sulfur chemolithotrophs, and sulfate-reducing bacteria for basic research and for biotechnological exploitation; and (3) reveal the most ecologically significant sulfur-cycling prokaryotes in Lake Fryxell and identify metabolically important organisms that remain to be cultured. In addition to advancing an understanding of the microbial sulfur cycle, the results of the proposed research will positively impact efforts to recognize and culture microbial life outside planet Earth, and should reveal the limits, in terms of low temperature, to which microbial sulfur-cycling can occur on Earth.