Sulfate-reducing bacterial community response to carbon source amendments in contaminated aquifer microcosms

Microbial sulfate reduction is an important metabolic activity in many reduced habitats. However, little is known about the sulfate-reducing communities inhabiting petroleum hydrocarbon (PHC)-contaminated freshwater aquifer sediments. The purpose of this study was to identify the groups of sulfate-reducing bacteria (SRB) selectively stimulated when sediment from a PHC-contaminated freshwater aquifer was incubated in sulfate-reducing aquifer microcosms that were amended with specific carbon sources (acetate, butyrate, propionate, lactate, and citrate). After 2 months of incubation, the SRB community was characterized using phospholipid fatty acid (PLFA) analysis combined with multivariate statistics as well as fluorescence in situ hybridization (FISH). Molybdate was used to specifically inhibit SRB in separate microcosms to investigate the contribution of non-SRB to carbon source degradation. Results indicated that sulfate reduction in the original sediment was an important process but was limited by the availability of sulfate. Substantially lower amounts of acetate and butyrate were degraded in molybdate treatments as compared to treatments without molybdate, suggesting that SRB were the major bacterial group responsible for carbon source turnover in microcosms. All of the added carbon sources induced changes in the SRB community structure. Members of the genus Desulfobulbus were present but not active in the original sediment but an increase of the fatty acids 15:1ω6c and 17:1ω6c and FISH results showed an enrichment of these bacteria in microcosms amended with propionate or lactate. The appearance of cy17:0 revealed that bacteria affiliated with the Desulfobacteriaceae were responsible for acetate degradation. Desulfovibrio and Desulfotomaculum spp. were not important populations within the SRB community in microcosms because they did not proliferate on carbon sources usually favored by these organisms. Metabolic, PLFA, and FISH results provided information on the SRB community in a PHC-contaminated freshwater environment, which exhibited stimulation patterns similar to other (e.g. marine) environment

Field-scale isotopic labeling of phospholipid fatty acids from acetate-degrading sulfate-reducing bacteria

Isotopic labeling of biomarker molecules is a technique applied to link microbial community structure with activity. Previously, we successfully labeled phospholipid fatty acids (PLFA) of suspended nitrate-reducing bacteria in an aquifer. However, the application of the method to low energy-yielding processes such as sulfate reduction, and extension of the analysis to attached communities remained to be studied. To test the feasibility of the latter application, an anoxic test solution of 500 l of groundwater with addition of 0.5 mM Br− as a conservative tracer, 1.1 mM SO2−4, and 2.0 mM [2-13C]acetate was injected in the transition zone of a petroleum hydrocarbon-contaminated aquifer where sulfate-reducing and methanogenic conditions prevailed. Thousand liters of test solution/groundwater mixture were extracted in a stepwise fashion after 2-46 h incubation. Computed apparent first-order rate coefficients were 0.31 ± 0.04 day−1 for acetate and 0.34 ± 0.05 day−1 for SO2−4 consumption. The δ13C increased from −71.03‰ to +3352.50‰ in CH4 and from −16.15‰ to +32.13‰ in dissolved inorganic carbon (DIC). A mass balance suggested that 43% of the acetate-derived 13C appeared in DIC and 57% appeared in CH4. Thus, acetate oxidation coupled to sulfate reduction and acetoclastic methanogenesis occurred simultaneously. The δ13C of PLFA increased on average by 27‰ in groundwater samples and 4‰ in sediment samples. Hence, both suspended and attached communities actively degraded acetate. The PLFA labeling patterns and fluorescent in situ hybridization (FISH) analyses of sediment and groundwater samples suggested that the main sulfate-reducing bacteria degrading the acetate were Desulfotomaculum acetoxidans and Desulfobacter sp. in groundwater, and D. acetoxidans in sedimen

Benzoate-driven dehalogenation of chlorinated ethenes in microbial cultures from a contaminated aquifer

Microbial dehalogenation of tetrachloroethene (PCE) and cis-dichloroethene (cis-DCE) was studied in cultures from a continuous stirred tank reactor initially inoculated with aquifer material from a PCE-contaminated site. Cultures amended with hydrogen and acetate readily dechlorinated PCE and cis-DCE; however, this transformation was incomplete and resulted in the accumulation of chlorinated intermediates and only small amounts of ethene within 60days of incubation. Conversely, microbial PCE and cis-DCE dechlorination in cultures with benzoate and acetate resulted in the complete transformation to ethene within 30days. Community fingerprinting by denaturing gradient gel electrophoresis (DGGE) revealed the predominance of phylotypes closely affiliated with Desulfitobacterium, Dehalococcoides, and Syntrophus species. The Dehalococcoides culture VZ, obtained from small whitish colonies in cis-DCE dechlorinating agarose cultures, revealed an irregular cell diameter between 200 and 500nm, and a spherical or biconcave disk-shaped morphology. These organisms were identified as responsible for the dechlorination of cis-DCE to ethene in the PCE-dechlorinating consortia, operating together with the Desulfitobacterium as PCE-to-cis-DCE dehalogenating bacterium and with a Syntrophus species as potential hydrogen-producing partner in cultures with benzoat

Sulfate-reducing bacterial community response to carbon source amendments in contaminated aquifer microcosms

ISSN:0168-6496ISSN:1574-694

Field-scale isotopic labeling of phospholipid acetate-degrading sulfate-reducing fatty acids from bacteria

ISSN:0168-6496ISSN:1574-694

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

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 sulfate-reducing zone of a PHC-contaminated aquifer

Benzoate-driven dehalogenation of chlorinated ethenes in microbial cultures from a contaminated aquifer

ISSN:0175-7598ISSN:1432-061