Roles of thermophilic thiosulfate-reducing bacteria and methanogenic archaea in the biocorrosion of oil pipelines

Thermophilic sulfide-producing microorganisms from an oil pipeline network were enumerated with different sulfur oxyanions as electron acceptors at 55 oC. Most-probable number (MPN) analysis showed that thiosulfate-reducing bacteria were the most numerous sulfidogenic microorganisms in pipeline inspection gauge (PIG) scrapings. Thiosulfate-reducing and methanogenic enrichments were obtained from the MPN cultures that were able to use yeast extract as the electron donor. Molecular analysis revealed that both enrichments harbored the same dominant bacterium, which belonged to the genus Anaerobaculum. The dominant archaeon in the methanogenic enrichment was affiliated with the genus Methanothermobacter. With yeast extract as the electron donor, the general corrosion rate by the thiosulfate-reducing enrichment (8.43 ± 1.40 milli-inch per year, abbreviated as mpy) was about 5.5 times greater than the abiotic control (1.49 ± 0.15 mpy), while the comparable measures for the methanogenic culture were 2.03 ± 0.49 mpy and 0.62 ± 0.07 mpy, respectively. Total iron analysis in the cultures largely accounted for the mass loss of iron measured in the weight loss determinations. Profilometry analysis of polished steel coupons incubated in the presence of the thiosulfate-reducing enrichment revealed 59 pits over an area of 71.16 mm2, while only 6 pits were evident in the corresponding methanogenic incubations. The results show the importance of thiosulfate-utilizing, sulfide-producing fermentative bacteria such as Anaerobaculum sp. in the corrosion of carbon steel, but also suggest that Anaerobaculum sp. are of far less concern when growing syntrophically with methanogens

Periplasmic Cytochrome c(3) of Desulfovibrio vulgaris Is Directly Involved in H(2)-Mediated Metal but Not Sulfate Reduction

Kinetic parameters and the role of cytochrome c(3) in sulfate, Fe(III), and U(VI) reduction were investigated in Desulfovibrio vulgaris Hildenborough. While sulfate reduction followed Michaelis-Menten kinetics (K(m) = 220 μM), loss of Fe(III) and U(VI) was first-order at all concentrations tested. Initial reduction rates of all electron acceptors were similar for cells grown with H(2) and sulfate, while cultures grown using lactate and sulfate had similar rates of metal loss but lower sulfate reduction activities. The similarities in metal, but not sulfate, reduction with H(2) and lactate suggest divergent pathways. Respiration assays and reduced minus oxidized spectra were carried out to determine c-type cytochrome involvement in electron acceptor reduction. c-type cytochrome oxidation was immediate with Fe(III) and U(VI) in the presence of H(2), lactate, or pyruvate. Sulfidogenesis occurred with all three electron donors and effectively oxidized the c-type cytochrome in lactate- or pyruvate-reduced, but not H(2)-reduced cells. Correspondingly, electron acceptor competition assays with lactate or pyruvate as electron donors showed that Fe(III) inhibited U(VI) reduction, and U(VI) inhibited sulfate loss. However, sulfate reduction was slowed but not halted when H(2) was the electron donor in the presence of Fe(III) or U(VI). U(VI) loss was still impeded by Fe(III) when H(2) was used. Hence, we propose a modified pathway for the reduction of sulfate, Fe(III), and U(VI) which helps explain why these bacteria cannot grow using these metals. We further propose that cytochrome c(3) is an electron carrier involved in lactate and pyruvate oxidation and is the reductase for alternate electron acceptors with higher redox potentials than sulfate

Municipal Solid Waste Landfills Harbor Distinct Microbiomes

Landfills are the final repository for most of the discarded material from human society and its built environments. Microorganisms subsequently degrade this discarded material in the landfill, releasing gases (largely CH4 and CO2) and a complex mixture of soluble chemical compounds in leachate. Characterization of landfill microbiomes and their comparison across several landfills should allow the identification of environmental or operational properties that influence the composition of these microbiomes and potentially their biodegradation capabilities. To this end, the composition of landfill microbiomes was characterized as part of an ongoing USGS national survey studying the chemical composition of leachates from 19 non-hazardous landfills across 16 states in the continental U.S. The landfills varied in parameters such as size, waste composition, management strategy, geography, and climate zone. The diversity and composition of bacterial and archaeal populations in leachate samples were characterized by 16S rRNA gene sequence analysis, and compared against a variety of physical and chemical parameters in an attempt to identify their impact on selection. Members of the Epsilonproteobacteria, Gammaproteobacteria, Clostridia, and candidate division OP3 were the most abundant. The distribution of the observed phylogenetic diversity could best be explained by a combination of variables and was correlated most strongly with the concentrations of chloride and barium, rate of evapotranspiration, age of waste, and the number of detected household chemicals. This study illustrates how leachate microbiomes are distinct from those of other natural or built environments, and sheds light on the major selective forces responsible for this microbial diversity

Metagenomic analysis and metabolite profiling of deep-sea sediments from the Gulf of Mexico following the Deepwater Horizon oil spill

Marine subsurface environments, such as deep-sea sediments, house abundant and diverse microbial communities that are believed to influence large-scale geochemical processes. These processes include the biotransformation and mineralization of numerous petroleum constituents. Thus, microbial communities in the Gulf of Mexico are thought to be responsible for the intrinsic bioremediation of crude oil released by the Deepwater Horizon (DWH) oil spill. While hydrocarbon contamination is known to enrich for aerobic, oil-degrading bacteria in deep-seawater habitats, relatively little is known about the response of communities in deep-sea sediments, where low oxygen levels may hinder such a response. Here, we examined the hypothesis that increased hydrocarbon exposure results in an altered sediment microbial community structure that reflects the prospects for oil biodegradation under the prevailing conditions. We explore this hypothesis using metagenomic analysis and metabolite profiling of deep-sea sediment samples following the DWH oil spill. The presence of aerobic microbial communities and associated functional genes was consistent among all samples, whereas, a greater number of Deltaproteobacteria and anaerobic functional genes were found in sediments closest to the DWH blowout site. Metabolite profiling also revealed a greater number of putative metabolites in sediments surrounding the blowout zone relative to a background site located 127 km away. The mass spectral analysis of the putative metabolites revealed that alkylsuccinates remained below detection levels, but a homologous series of benzylsuccinates (with carbon chain lengths from 5 to 10) could be detected. Our findings suggest that increased exposure to hydrocarbons enriches for Deltaproteobacteria, which are known to be capable of anaerobic hydrocarbon metabolism. We also provide evidence for an active microbial community metabolizing aromatic hydrocarbons in deep-sea sediments of the Gulf of Mexi