Abstract:

Diverse microorganisms play important roles in biogeochemical cycles in estuaries. In order to identify the potential impacts of oil contamination on microbial groups that control critical biogeochemical cycles in estuarine sediments, the concentrations of genes involved in nitrogen and carbon cycling were compared in oiled and unoiled areas of Bay Jimmy, LA. Total bacterial numbers were higher by a factor of two in unoiled than in oiled surface sediments (0-2 cm sections), regardless of the degree of oiling (high vs low). The numbers converged in 2-4 cm and deeper sections, however, suggesting impacts of oil may be limited to the surface sections. Similar trends were observed with concentrations of nifH, characteristic of nitrogen fixation. More significant impacts were observed with genes representing sulfate reduction (dsrB) and nitrate reduction (nirS and nirK), which showed significant decreases to the 4-6 cm depths. The impact of oil on concentrations of genes characteristic of methanogens (mcrA) increased with depth, possibility due to availability of electron donors. These trends suggest that the impacts of oil on sediment microbial communities may be complex. Further work is required to determine the mechanisms behind these trends. Exposure to oil resulted in decrease species richness and diversity of sulfate reducers while increasing those of denitrifiers (even though total numbers declined), indicating that oil impacts on microbial communities are complex. In conclusion, oil spill influenced the population sizes and assemblage structures of prokaryotes in complex ways.

Suggested Citation:

Andrew Ogran, Hee-Sung Bae. 2015. Impact of oil on concentrations of microbial genes related to carbon and nitrogen cycling in Bay Jimmy, LA, sediments. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7WH2MZD

Purpose:

Culture independent molecular approach was performed to assess the impact of oil spill on changes of microbes involved in biogeochemical cycles such as carbon and nitrogen cycles. A real-time PCR was used for quantifying the functional groups of microbes involved in nitrate reduction (nirK/nirS), nitrogen fixation (nifH), ammonia oxidation (amoA), sulfate reduction (dsrB), methanogenesis (mcrA). Clone library analysis was performed to assess the diversity and distribution of denitrification and sulfate reducers.

Data Parameters and Units:

Phylotype richness estimators and diversity index of gen dsrB and nirS assayed from the upper sediment of unoiled and oiled sediment of Bay Jimmy, LA. Gene [dsrB, nirS], Study Site, screened, Number of Phylotypes (count), estimator, Shannon's diversity index, Coverage (%). Figures 1-5. qPCR results. Target organism [ammonia oxydizing archaea, ammonia oxydizing bacteria, nitrate reducing bacteria, N2-fixing prokaryotes, SO4-reducing prokaryotes, Methanogens, Total bacteria], Gene, depth (cm), gene copy number/g soil in control sites, gene copy number/g soil in oiled sites.

Individual Files: