| Summary: | 학위논문 (박사)-- 서울대학교 대학원 자연과학대학 생명과학부, 2017. 8. 김상종. Antarctica has been considered as pristine and harsh environment in respect to microbes because of the extreme conditions. Perennially ice-covered lakes (Lake Fryxell, Lake Miers, and Lake Bonney) in the McMurdo Dry Valleys, Antarctica, are chemically stratified with depth and have distinct biological gradients. Despite of long-term research on these unique environments, the information on the structure of the microbial communities in the water columns of these lakes are scarce. In this study, bacterial diversity in the ice-covered lakes in Antarctica was examined by 16S rRNA gene-based pyrosequencing. Distinct communities were present in each lake, reflecting the unique biogeochemical characteristics of these environments. Further, certain bacterial lineages were exclusively confined to specific depths within each lake. For example, candidate division WM88 occurred solely at a depth of 15 m in Lake Fryxell, whereas unknown lineages of Chlorobi were found only at a depth of 18 m in Lake Miers, and two distinct classes of Firmicutes inhabited East and West Lobe Bonney at depth of 30 m. Redundancy analysis revealed that community variation of bacterioplankton could be explained by the distinct conditions of each lake and depth in particular, assemblages from layers beneath the chemocline had biogeochemical associations that differed from those in the upper layers. Despite of the fact that sulfate reduction has been actively detected, little is known about diversity of sulfate reducing bacteria in Lake Fryxell. Less than 1% of total bacteria are known to be culturable. By application of culture-independent approach such as metagenomics, not only full extent of bacterial diversity but also their ecological function could be obtained. Three draft genomes were recovered from metagenome data as sulfate reduction-related bacteria, two belonging to Deltaproteobacteria and one belonging to candidate division WM88. Deltaproteobacteria was a key player for sulfate ...
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