| Summary: | Compared to other microbes such as Bacteria or algae, our knowledge of archaeal biology is limited. The most abundant Archaea in the oceans are the Marine Groups I, II, and III. Previous studies have found that the biogeographical distributions of each group are distinct, specific, and consistent within the groups. The differences in spatial distributions are suggested to be influenced by light penetration and temperature. Temperature greatly affects the biochemical processes and physiological states of microorganisms. Many indices have been developed to detect temperature adaptation in thermophilic microbes, however, this becomes much more difficult for microbes living in low temperature environments. Metagenomic sequence data was collected from seawater in the Western Arctic Ocean during the GEOTRACES 2015 expedition. This thesis aims to categorize the distributions patterns of archaeal MAGs in relation to their biogeography and proteomic presentations. Members of all three marine groups were identified and it was determined that their relative abundances were highly connected with Arctic stratification and water mass layers. Additionally, it was observed here for the first time that bins from all three marine groups displayed variable distribution ecotypes. Using a collection of archaeal genomes from the Bacterial and Viral Bioinformatics Resource Center database, amino acid compositional indices were used to detect signatures of cold adaptation in their proteomes. Although signatures of cold adaptation were not detected, it was determined that there were differences based on the phylogenetics and environmental sources. Higher arginine to lysine ratios were observed in the sequences collected from sea sponges, further supported by significant differences observed in the codon usage and amino acid presence, suggesting a strong selective pressure to obtain host-adaptation. Overall, this thesis contributes to our understanding of archaeal ecology, especially in an understudied environment like the Arctic Ocean. ...
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