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Microbial community dynamics in Saanich Inlet : insights into population structure and methane cycling in a seasonally anoxic fjord Stilwell, Claire Patricia

Abstract

As the importance of oceanic environments to the regulation of global energy and nutrient dynamics is better understood, the critical role marine microbial communities play in cycling nutrients and regulating gas flux from oceans is becoming more apparent. With the prediction that rising atmospheric temperatures will cause an overall decrease in marine oxygen levels, the oxygen minimum zones (OMZ's) of today may represent oceanic environments of the future. To better understand the microbial dynamics of these environments, I undertook a spatial and temporal study of the microbial community in the water column of Saanich Inlet, a model OMZ. This inlet is seasonally anoxic, and is notable for microbial regulation of methane flux to the atmosphere. The microbial community was sampled in February 2006 at 4 depths spanning the oxycline, and molecular taxonomic analysis revealed that the bacterial groups present were very similar to other OMZ's. Overall, the proteobacteria were most abundant and sequences similar to Type-I and Type-II methanotrophs were detected at 10 m and 100 m. Relatives of sulfur-oxidizing bacterial endosymbionts, commonly found in other OMZ's almost completely dominated the community at 215 m. However, the absence of epsilon proteobacteria linked to sulfide oxidation was in contrast to other OMZ's. Members of the crenarchaea dominated the water column; and no methanogens or ANME groups belonging to the euryarchaea were detected. However, novel pmoA phylotypes detected at all 4 depths in Saanich Inlet, showed a depth distribution suggesting that aerobic methane oxidation is the primary component of the methane cycle occurring in the water column. Temporal data suggested that the microbial community is relatively stable and primarily distributed according to depth, and that methane and oxygen concentrations contribute to this distribution. Notably, a late summer deep-water turnover event in Saanich Inlet did affect the distribution of the microbial communities at 200 m.

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