ROLE OF MICROBIAL COMMUNITY STRUCTURE AND FUNCTION IN BTEX BIODEGRADATION AT THE BEMIDJI CRUDE-OIL SPILL SITE (Invited Presentation)

Differences in biodegradation rates of benzene, toluene, ethylbenzene, and xylene(s) (BTEX) were previously observed in in-situ microcosms (ISMs) installed in wetland versus iron reducing aquifer sediment at the Bemidji, MN Crude-Oil Spill site. Molecular tools can complement geochemical analyses providing insight into the conditions driving biodegradation and the ultimate fate of these contaminants. Molecular microbiological analyses were performed on two sample sets from Bemidji site: (1) ISMs performed in wetland sediments comparing BTEX biodegradation under natural and nitrate-stimulated conditions in summer 2010 and (2) sediment cores collected in summer 2012 from the wetland and methanogenic and iron reducing zones of the aquifer. Bacterial community structure was explored with denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes. Functional analysis was performed using quantitative PCR (qPCR) targeting metabolic genes of interest related to methanogenesis (mcrA) and sulfate reduction (dsrA) as well as genes relevant to the common anaerobic degradation pathway, benzoyl-coenzyme A (CoA) pathway. Specifically, assays were performed for benzoyl-CoA reductases in facultative anaerobes (bcrC, bzdN) and obligate anaerobes (bamB), and for ring-cleaving hydrolase (bamA). Results for ISMs indicate significantly different community structures in nitrate-treated and non-treated microcosms. mcrA gene copies increased across the duration of the experiment only in the sediments not stimulated by nitrate. These results agree with geochemical observations for ISMs: more methane production was observed in un-stimulated compared to nitrate-stimulated sediments. Further, differences in microbial community structure and function may correspond to differences in biodegradation rates. Core sample profiling indicates that spatial heterogeneity in microbial communities exists at the site, further challenging prediction of natural attenuation progress and plume modeling.