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Effects of hypoxia on archaeal communities in Gulf of Mexico sediments
Citation:
PALUMBO, A. V., J. J. MOSHER, T. A. VISHNIVETSKAYA, D. L. BEDDICK, D. F. YATES, S. D. BROWN, AND R. DEVEREUX. Effects of hypoxia on archaeal communities in Gulf of Mexico sediments . Presented at 112th General Meeting of the American Society for Microbiology, San Francisco, CA, June 16 - 19, 2012.
Impact/Purpose:
Presentataion for 112th General Meeting of American Society for Microbiology
Description:
Sediments may contribute significantly to Louisiana continental shelf “dead zone” hypoxia but limited information hinders understanding how sediment biogeochemistry differs between normoxic and hypoxic seasons. Archaea of the family Thaumarchaeota are largely responsible for nitrification in marine environments. Thaumarchaeota community structure might, therefore, provide insights into effects of hypoxia on nitrogen cycling in dead zone sediments. Replicate sediment cores were collected south of Terrebone Bay in April (oxic) and September (hypoxic) 2006. Cores were sliced into 2 cm depth intervals under anoxic conditions and a suite of geochemical parameters, including Fe, Mn, and nutrients were measured in each fraction. Pyrosequencing analysis of the 16S rRNA V4 hypervariable region using Titanium chemistry was performed on DNA extracted from the sediments to determine archaeal community structure. Of the geochemical parameters, dissolved inorganic carbon (p<0.001), NH4 (p<0.001), porewater Fe2+ (p=0.033), NO2 (p=0.03), NOx (p=0.003), PO4 (p<0.001) and solid Fe II (p=0.001) were found in significantly greater concentrations in the September (hypoxic) sediment samples. Porewater Mn (p=0.011) and solid Fe III (p=0.001) concentrations were significantly greater in the April (normoxic) sediment samples. Crenarchaeote sequences accounted for over half of the 260,000 sequences obtained. The most abundant cluster of genus-level (97% similarity) sequences was related to an uncultured Desulfurococcaceae. Sequences within the cluster accounted for 11% of all those obtained. They were most abundant in the deepest sediment core fractions (6 to 10 cm) collected during hypoxic conditions in September. The next three most abundant clusters were comprised of ammonium-oxidizing Thaumarchaeota. Nitrosopumilus accounted for 15% of the total sequences. Nitrosopumilus clusters were most abundant in the upper 6 cm of sediment and were significantly higher in cores collected under normoxic conditions. Thus, the abundance of Nitrosopumilus spp. may be related to the availability of oxygen needed for ammonium oxidation. These results document changes in sediment geochemistry and the community structure of Archaea brought on by periods of hypoxic bottom waters in the Gulf of Mexico.