Predominance of Methanolobus spp. and Methanoculleus spp. in the Archaeal Communities of Saline Gas Field Formation Fluids

The microbial communities in sulfate-rich, saline formation fluids of a natural gas reservoir in Lower Saxony, Germany were investigated to enhance the knowledge about microbial communities in potential carbon dioxide sequestration sites. This investigation of the initial state of the deep subsurface microbiota is necessary to predict their influence on the long-term stability and storage capacity of such sites. While the bacterial 16S rDNA gene library was comprised of sequences affiliating with the Firmicutes, the Alphaproteobacteria, the Gammaproteobacteria and the Thermotogales, the archaeal 16S rDNA libraries were simply dominated by two phylotypes related to the genera Methanolobus and Methanoculleus. The monitoring of the archaeal communities in different formation fluid samples by T-RFLP and Real-Time-PCR indicated that these two methanogenic genera dominated at all, whereas the proportion of the two groups varied. Thus, methylotrophic and autotrophic methanogenesis seems to be of importance in the reservoir fluids, dependent on the provided reduction equivalents and substrates and it also may influence the fate of CO₂ in the subsurface.     

Comparison of phylogenetic relationships based on phospholipid fatty acid profiles and ribosomal RNA sequence similarities among dissimilatory sulfate-reducing bacteria

Abstract Twenty-five isolates of dissimilatory sulfate-reducing bacteria were clustered based on similarity analysis of their phospholipid ester-linked fatty acids (PLFA). Of these, 22 showed that phylogenetic relationships based on the sequence similarity of their 16S rRNA directly paralleled the PLFA relationships. Desulfobacter latus and Desulfobacter curvatus grouped with the other Desulfobacter spp. by 16S rRNA comparison but not with the PLFA analysis as they contained significantly more monoenoic PLFA than the others. Similarly, Desulfovibrio africanus clustered with the Desulfovibrio spp. by 16S rRNA but not with them when analyzed by PLFA patterns because of higher monoenoic PLFA content. Otherwise, clustering obtained with either analysis was essentially congruent. The relationships defined by PLFA patterns appeared robust to shifts in nutrients and terminal electron acceptors. Additional analyses utilizing the lipopolysaccharide-lipid A hydroxy fatty acid patterns appeared not to shift the relationships based on PLFA significantly except when completely absent, as in Gram-positive bacteria. Phylogenetic relationships between isolates defined by 16S rRNA sequence divergence represent a selection clearly different from the multi-enzyme activities responsible for the PLFA patterns. Determination of bacterial relationships based on different selective pressures for various cellular components provides more clues to evolutionary history leading to a more rational nomenclature.     

Intraspecies variability of Desulfovibrio desulfuricans strains determined by the genetic profiles

Fifteen (soil and intestinal) strains of Desulfovibrio desulfuricans species were typed by PCR method with the use of primers specific for repetitive extragenic palindromic (REP) and enterobacterial repetitive intergenic consensus (ERIC) sequences. As a result, characteristic DNA fingerprints for the strains were obtained. Moreover, the genetic profiles were found to be useful for typing and distinguishing the strains of D. desulfuricans. According to cluster analysis, PCR with primers complementary to the sequences REP appeared to be slightly more discriminatory than PCR with ERIC primers for the investigated strains. Distinct fingerprint patterns of two isolates derived from the same patient pointed to the different origin of both strains.     

The relationship between hydrogen metabolism,sulfate reduction and nitrogen fixation in sulfate reducers

Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D₂–H⁺ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism.     

Dimethylsulfoxide reduction by marine sulfate-reducing bacteria

Abstract Dimethylsulfoxide (DMSO) reduction occurred in five out of nine strains of sulfate-reducing bacteria from marine or saline environments, but not in three freshwater isolates. DMSO reduction supported growth in all positive strains. In Desulfovibrio desulfuricans strain PA2805, DMSO reduction occurred simultaneously with sulfate reduction and was not effectively inhibited by molybdate, a specific inhibitor of sulfate reduction. The growth yield per mol lactate was 26% higher with DMSO than with sulfate as electron acceptor. In extracts of cells of strain PA2805 grown on sulfate, a low level of DMSO-reducing activity was present (0.013 μmol (mg protein)⁻ min⁻); higher levels were found in cells grown on DMSO (0.56 μmol (mg protein)⁻ min⁻). In anoxic marine environments DMSO reduction by sulfate-reducing bacteria may lead to enhanced dimethylsulfide emission rates.     

Whole-cell antigens of members of the sulfate-reducing genus Desulfovibrio

Antisera have been developed against the wholecell antigens of Desulfovibrio africanus Benghazi and Walvis Bay, D. vulgaris Hildenborough, D. salexigens British Guiana, D. gigas, and D. desulfuricans Essex 6. An enzymelinked immunoadsorption assay (ELISA) was developed to measure the reaction of these antisera with the homologous and heterologous antigens. The ELISA method demonstrated a reaction between pre-immune sera and cells of D. africanus, D. gigas and D. desulfuricans, suggesting the presence of a lectin-like substance on these cell surfaces. Extensive cross-reactions were seen between the antisera and heterologous cells, suggesting the sharing of a number of surface antigens amongst the Desulfovibrio. However, the pattern of these cross-reactions was different from that observed for an ELISA reaction developed for the cytochrome c₃ from various Desulfovibrio.Abbreviation ELISA enzyme-linked immunoadsorption assay     

The use of magnesium peroxide for the inhibition of sulfate-reducing bacteria under anoxic conditions

Sulfate-reducing bacteria (SRB), which cause microbiologically influenced material corrosion under anoxic conditions, form one of the major groups of microorganisms responsible for the generation of hydrogen sulfide. In this study, which is aimed at reducing the presence of SRB, a novel alternative approach involving the addition of magnesium peroxide (MgO₂) compounds involving the use of reagent-grade MgO₂ and a commercial product (ORC™) was evaluated as a means of inhibiting SRB in laboratory batch columns. Different concentrations of MgO₂ were added in the columns when black sulfide sediment had appeared in the columns. The experimental results showed that MgO₂ is able to inhibit biogenic sulfide. The number of SRB, the sulfide concentration and the sulfate reducing rate (SRR) were decreased. ORC™ as an additive was able to decrease more effectively the concentration of sulfide in water and the SRB-control effect was maintained over a longer time period when ORC™ was used. The level of oxidation–reduction potential (ORP), which has a linear relationship to the sulfide/sulfate ratio, is a good indicator of SRB activity. As determined by fluorescence in-situ hybridization (FISH), most SRB growth was inhibited under increasing amounts of added MgO₂. The concentration of sulfide reflected the abundance of the SRB. Utilization of organic matter greater than the theoretical SRB utilization rate indicated that facultative heterotrophs became dominant after MgO₂ was added. The results of this study could supply the useful information for further study on evaluating the solution to biocorrosion problems in practical situations.     

Cloning in Escherichia coli of genes involved in the synthesis of proline and leucine in Desulfovibrio desulfuricans Norway

Summary A library of Deusulfovibrio desulfuricans Norway genomic DNA was constructed in Escherichia coli with pBR322 as vector and plasmids able to complement the proA and leuB mutations of the host were screened. It was observed that all the plasmids studied were highly unstable, the insert DNA being rapidely lost under non-selective growth conditions. A 2.75 kb DNA fragment of D. desulfuricans Norway was found to complement E. coli ProA, ProB and ProC deficiencies. From the results of restriction analysis and Southern hybridization, it is proposed that the genes involved in proline and leucine biosynthesis are clustered on the chromosome of D. desulfuricans Norway.