Activity and Diversity of Sulfate-Reducing Bacteria in a Petroleum Hydrocarbon-Contaminated Aquifer

Abstract

Microbial sulfate reduction is an important metabolic activity in petroleum hydrocarbon (PHC)-contaminated aquifers. We quantified carbon source-enhanced microbial SO 4 2؊ reduction in a PHC-contaminated aquifer by using single-well push-pull tests and related the consumption of sulfate and added carbon sources to the presence of certain genera of sulfate-reducing bacteria (SRB). We also used molecular methods to assess suspended SRB diversity. In four consecutive tests, we injected anoxic test solutions (1,000 liters) containing bromide as a conservative tracer, sulfate, and either propionate, butyrate, lactate, or acetate as reactants into an existing monitoring well. After an initial incubation period, 1,000 liters of test solution-groundwater mixture was extracted from the same well. Average total test duration was 71 h. We measured concentrations of bromide, sulfate, and carbon sources in native groundwater as well as in injection and extraction phase samples and characterized the SRB population by using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE). Enhanced sulfate reduction concomitant with carbon source degradation was observed in all tests. Computed first-order rate coefficients ranged from 0.19 to 0.32 day ؊1 for sulfate reduction and from 0.13 to 0.60 day ؊1 for carbon source degradation. Sulfur isotope fractionation in unconsumed sulfate indicated that sulfate reduction was microbially mediated. Enhancement of sulfate reduction due to carbon source additions in all tests and variability of rate coefficients suggested the presence of specific SRB genera and a high diversity of SRB. We confirmed this by using FISH and DGGE. A large fraction of suspended bacteria hybridized with SRB-targeting probes SRB385 plus SRB385-Db (11 to 24% of total cells). FISH results showed that the activity of these bacteria was enhanced by addition of sulfate and carbon sources during push-pull tests. However, DGGE profiles indicated that the bacterial community structure of the dominant species did not change during the tests. Thus, the combination of push-pull tests with molecular methods provided valuable insights into microbial processes, activities, and diversity in the sulfatereducing zone of a PHC-contaminated aquifer. Dissimilatory microbial SO 42Ϫ reduction is an important metabolic activity in many reduced environments, such as marine sediments (22), anaerobic sludge (28), and contaminated aquifers (25). This process is mediated by a metabolically diverse group of microorganisms: the sulfate-reducing bacteria (SRB) (31,35,51). SRB were found to grow on environmental contaminants such as petroleum hydrocarbon (PHC) constituents (e.g., benzene, toluene, ethylbenzene, xylenes, naphthalene, phenanthrene, and alkanes) and halogenated compounds (15,55). A survey of 38 PHC-contaminated aquifers revealed that on average, SO 4 2Ϫ reduction was responsible for 70% of PHC attenuation (53).During the degradation of PHC, low-molecular-weight organic acids such as acetate, propion...

Community Composition and Functioning of Denitrifying Bacteria from Adjacent Meadow and Forest Soils

“…5). over in community structure, can be associated with relatively large differences in biogeochemical processes (17,20,34). We found denitrification activity an order of magnitude higher in meadow than in forest soils and a significant shift in the proportional abundances of dominant denitrifying genotypes (i.e., nosZ RsaI 666-and 700-bp T-RFs) from meadow to forest soils.…”

Regime Shift and Microbial Dynamics in a Sequencing Batch Reactor for Nitrification and Anammox Treatment of Urine

“…At each time point, 1-ml samples of suspended biomass were taken from the reactor with a micropipette, mixed with 10% of a nucleic acid preserving solution (95% ethanol, 5% buffered phenol [7]), centrifuged, and decanted, and the pellets were frozen at Ϫ80°C until further processing. DNA was extracted with a bead-beating method described previously (24) with some modifications. Briefly, 0.5 ml sample and 1.5 ml lysis buffer (50 mM Tris [pH 8], 50 mM EDTA, 50 mM sodium chloride) were lysed by bead beating (3 times for 80 s each time at 3,000 rpm using 0.2 g 106-m-and 0.2 g 150-to 212-m-diameter beads), followed by chemical and enzymatic lysis with 10 mg ml Ϫ1 lysozyme (final concentration) for 10 min and with 1% SDS and 3,600 U ml Ϫ1 proteinase K for 30 min.…”

Subsurface ecosystem resilience: long-term attenuation of subsurface contaminants supports a dynamic microbial community

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