N-121. Prokaryotic Diversity in an Oxygen Minimum Zone off the Coast of Oregon

A. D. Bertagnolli, A. H. Treush, O. U. Mason, U. Stingl, K. Vergin, F. T. Chan, S. J. Giovannoni;
Oregon State Univ., Corvallis, OR.

Background: The inner shelf region of the Northeast Pacific Ocean is a highly productive ecosystem that experiences upwelling events on a yearly basis. Upwelling spurs increases in productivity, resulting in microbial respiration rates that deplete dissolved oxygen concentrations, thus creating oxygen minimum zones (OMZs). The goal of this study was to determine how prokaryotic communities change in response to low oxygen conditions in the water column off the Oregon Coast. Methods: We used terminal restriction fragment length polymorphism analysis (tRFLP) as well as clone libraries of DNA amplified from the small subunit 16S rRNA gene from filtered water samples to examine shifts in prokaryotic lineages at station SH50 (44.25o, 124.2o) at three depths (5m, 20m, 40m) during the summer of 2007, prior to, during and after OMZ formation. Results: tRFLP profiles collected during a hypoxic event (July 11th 2007) suggested that bacterial community structure varies spatially, with the most pronounced differences occurring between samples collected from depths of 5 m and 40 m, which correspond to high and low oxygen environments, respectively. The relative abundance of bacterial lineages that typically dominate oceanic microbial communities, such as the SAR11 clade, decreased over all depths, while Roseobacter, Bacteriodetes and marine Actinobacteria were more prevalent in the deepest, most oxygen depleted location. 16S rDNA clone library construction and sequencing yielded evidence of a diversity of prokaryotes within the OMZ, including members of the α-, γ-proteobacteria, Planctomycetes, and Verrucomicrobia. Conclusions: Our results suggest that the stress of low oxygen conditions does affect prokaryotic community structure. These perturbations may have cascading effects on coastal nutrient cycling.