Paper No. 6
Presentation Time: 9:00 AM-6:00 PM
BACTERIAL DIVERSITY AND HETEROTROPHIC BIODEGRADATION RATE FROM COASTAL MARSHES IN GULF OF MEXICO
The 2010 Deepwater Horizon oil spill in the Gulf of Mexico not only impacted open ocean and shoreline geochemical and ecological environments, but it served to promote research of microbial ecosystems in poorly studied habitats, such as Louisiana marshes. Sediment and water samples from twelve marshes in southern Louisiana were collected in May 2010 (pre-oil), September 2010 (oiled), and July 2011 (post-oil). Microbial diversity, evaluated from tag-encoded FLX-amplicon pyrosequencing, increased slightly from pre- to post-oil sampling times, but the main taxonomic groups between pre- and post-oil samples shifted. Proteobacteria (Gammaproteobacteria and Betaproteobacteria), Bacteriodetes, and Firmicutes were represented in the pre-oil samples, but Firmicutes dominated almost all oiled samples from the same locations. Some known hydrocarbon-degraders observed in pre-oil samples included Acinetobacter, Bacillus, and Flavobacteria spp. Their abundances increased in oiled samples having avg. total alkane concentrations of 254 mg/kg (n = 29) and avg. aromatic concentrations of 4.9 mg/kg (n = 26), compared to below detection values in pre-oil samples. Rates of community-level, heterotrophic hydrocarbon degradation were examined by incubating marsh sediments at 25 and 4 oC with different substrates. The maximum specific growth rate on glucose at 25 oC was three times higher than at 4 oC, which also lagged three days behind the warmer temperature. These results are being used to test the hypothesis that continued exposure to hydrocarbons will slow degradation rates unless there are shifts in the microbial diversity capable of degrading hydrocarbons. This study provides a comprehensive investigation of the diversity of microbial communities in marsh sediments over a period of one year, which has not been previously done. Collectively, the results will aid in our understanding of how microbial ecosystems can respond to hydrocarbon contamination.