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UBC Theses and Dissertations

Microbial community structure and ecology of Marine Group A bacteria in the oxygen minimum zone of the Northeast subarctic Pacific Ocean Wright, Jody Jennifer


Oxygen minimum zones (OMZs) are intrinsic water column features that arise when the respiratory oxygen (O2) demand during microbial remineralization of organic matter exceeds O2 supply rates in poorly ventilated regions of the ocean. Microbial processes play a key role in mediating biogeochemical cycling of nutrients and radiatively active trace gases in OMZs. Specific roles of individual microbial groups and the ecological interactions among groups that drive OMZ biogeochemistry on a global scale, however, remain poorly constrained. This dissertation focuses on describing microbial community structure in the world’s largest and least studied OMZ, located in the Northeast subarctic Pacific Ocean (NESAP), with a specific emphasis on characterizing the ecology of Marine Group A, an uncultivated candidate phylum of bacteria found to be prevalent in this region. To begin, I performed a survey of microbial community structure in the NESAP at two time points and over a range of depths based on traditional ecological analyses. I applied techniques derived from network theory to identify co-occurrence patterns among microbial groups within the NESAP and determined that MGA bacteria most frequently co-occurred with other MGA bacteria, suggesting that intra-phylum interactions may play a role in governing microbial processes in this region. Through analysis of small subunit ribosomal rRNA (SSU rRNA) gene sequences affiliated with MGA, I identified 8 novel subgroups and established the phylogeny and population structure of both novel and previously detected MGA subgroups. Finally, I provided first insights into the metabolic capacity of this little-known candidate phylum through investigations of metagenomic data obtained from NESAP waters. Analysis of large-insert genomic DNA fragments derived from MGA revealed protein-coding genes associated with adaptation to oxygen deficiency and sulfur-based energy metabolism. These observations may implicate MGA bacteria in the cryptic sulfur cycle, recently discovered to play a central role in biogeochemical cycling within OMZs. This work describes the first survey of microbial community structure in the NESAP OMZ and the first application of co-occurrence networks to study the ecology of deep ocean microbial communities, in addition to the first analysis of the diversity, population structure, and metabolic capacity of the enigmatic bacterial lineage MGA.

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