One-step process for debromination and aerobic mineralization of tetrabromobisphenol-A by a novel Ochrobactrum sp. T isolated from an e-waste recycling site

A novel bacterium, Ochrobactrum sp. T, capable of simultaneous debromination and aerobic mineralization of tetrabromobisphenol-A (TBBPA), was isolated from a sludge sample collected from an electronic-waste recycling site. The bacterium exhibited maximal debrominase activity at pH 6.5, 35 °C, and 200 rpm in Luria-Bertani culture medium. Initial TBBPA concentration and pH had more significant effects on degradation efficiency than those of temperature and inoculum size. Degradation and debromination efficiencies of 91.8% and 86.7%, respectively, were achieved within 72 h under optimized conditions of 35 °C, pH 7.0, inoculum volume of 25 mL, and TBBPA concentration of 3 mg L⁻¹. In addition, a 35.6% decrease in total organic carbon was observed after the degradation of 5 mg L⁻¹ TBBPA for 120 h. Eight metabolic intermediates were identified during the biodegradation of TBBPA. This study is the first report to propose a one-step process for TBBPA debromination and mineralization by a single bacterial strain.     

Changes in northern Gulf of Mexico sediment bacterial and archaeal communities exposed to hypoxia

Biogeochemical changes in marine sediments during coastal water hypoxia are well described, but less is known about underlying changes in microbial communities. Bacterial and archaeal communities in Louisiana continental shelf (LCS) hypoxic zone sediments were characterized by pyrosequencing 16S rRNA V4‐region gene fragments obtained by PCR amplification of community genomic DNA with bacterial‐ or archaeal‐specific primers. Duplicate LCS sediment cores collected during hypoxia had higher concentrations of Fe(II), and dissolved inorganic carbon, phosphate, and ammonium than cores collected when overlying water oxygen concentrations were normal. Pyrosequencing yielded 158 686 bacterial and 225 591 archaeal sequences from 20 sediment samples, representing five 2‐cm depth intervals in the duplicate cores. Bacterial communities grouped by sampling date and sediment depth in a neighbor‐joining analysis using Chao–Jaccard shared species values. Redundancy analysis indicated that variance in bacterial communities was mainly associated with differences in sediment chemistry between oxic and hypoxic water column conditions. Gammaproteobacteria (26.5%) were most prominent among bacterial sequences, followed by Firmicutes (9.6%), and Alphaproteobacteria (5.6%). Crenarchaeotal, thaumarchaeotal, and euryarchaeotal lineages accounted for 57%, 27%, and 16% of archaeal sequences, respectively. In Thaumarchaeota Marine Group I, sequences were 96–99% identical to the Nitrosopumilus maritimus SCM1 sequence, were highest in surficial sediments, and accounted for 31% of archaeal sequences when waters were normoxic vs. 13% of archaeal sequences when waters were hypoxic. Redundancy analysis showed Nitrosopumilus‐related sequence abundance was correlated with high solid‐phase Fe(III) concentrations, whereas most of the remaining archaeal clusters were not. In contrast, crenarchaeotal sequences were from phylogenetically diverse lineages, differed little in relative abundance between sampling times, and increased to high relative abundance with sediment depth. These results provide further evidence that marine sediment microbial community composition can be structured according to sediment chemistry and suggest the expansion of hypoxia in coastal waters may alter sediment microbial communities involved in carbon and nitrogen cycling.     

Characterization of an alkane-degrading methanogenic enrichment culture from production water of an oil reservoir after 274 days of incubation

Oil reservoirs represent special habitats for the activity of anaerobic microbial communities in the transformation of organic compounds. To understand the function of microbial communities in oil reservoirs under anaerobic conditions, an alkane-degrading methanogenic enrichment culture was established and analyzed. Results showed that a net 538 ??mol of methane higher than the controls were produced over 274 days of incubation in microcosms amended with alkanes and a decrease in the alkanes profile was also observed. Phylogenetic analysis of 16S rRNA gene sequences retrieved from the enrichment microcosms indicated that the archaeal phylotypes were mostly related to members of the orders Methanobacteriales and Methanosarcinales. The bacterial clone library was composed of sequences affiliated with the Firmicutes, Proteobacteria, Deferribacteres, and Bacteroidetes. However, most of the bacterial clones retrieved from the enrichment cultures showed low similarity to 16S rRNA gene sequences of the cultured members, indicating that the enrichment cultures contained novel bacterial species. Though alkane-degrading methanogenic enrichment consortium has rarely been reported from petroleum reservoirs, our results indicated that oilfield production water harbors a microbial community capable of syntrophic conversion of n-alkanes to methane, which sheds light on the bio-utilization of marginal oil reservoirs for enhanced energy recovery.     

Molecular characterization of microbial communities in deep coal seam groundwater of northern Japan

We investigated microbial methanogenesis and community structure based on 16S rRNA gene sequences from a coal seam aquifer located 843–907 m below ground level in northern Japan; additionally, we studied the δ¹³C and δ²H (δD) of coal‐bed gases and other physicochemical parameters. Although isotopic analysis suggested a thermocatalytic origin for the gases, the microbial activity and community structure strongly implied the existence of methanogenic microbial communities in situ. Methane was generated in the enrichment cultures of the hydrogenotrophic and methylotrophic microorganisms obtained from coal seam groundwater. Methanogen clones dominated the archaeal 16S rRNA gene libraries and were mostly related to the hydrogenotrophic genus Methanoculleus and the methylotrophic genus Methanolobus. Bacterial 16S rRNA gene libraries were dominated by the clones related to the genera Acetobacterium and Syntrophus which have a symbiotic association with methanogens. LIBSHUFF analysis revealed that N₂ gas injected into the coal seam (for enhanced methane production) does not affect the coverage of archaeal and bacterial populations. However, amova analysis does provide evidence for a change in the genetic diversity of archaeal populations that are dominated by methanogens. Therefore, N₂ injection into the coal seam might affect the cycling of matter by methanogens in situ.     

Prokaryotic diversity,composition structure,and phylogenetic analysis of microbial communities in leachate sediment ecosystems

In order to obtain insight into the prokaryotic diversity and community in leachate sediment, a culture-independent DNA-based molecular phylogenetic approach was performed with archaeal and bacterial 16S rRNA gene clone libraries derived from leachate sediment of an aged landfill. A total of 59 archaeal and 283 bacterial rDNA phylotypes were identified in 425 archaeal and 375 bacterial analyzed clones. All archaeal clones distributed within two archaeal phyla of the Euryarchaeota and Crenarchaeota, and well-defined methanogen lineages, especially Methanosaeta spp., are the most numerically dominant species of the archaeal community. Phylogenetic analysis of the bacterial library revealed a variety of pollutant-degrading and biotransforming microorganisms, including 18 distinct phyla. A substantial fraction of bacterial clones showed low levels of similarity with any previously documented sequences and thus might be taxonomically new. Chemical characteristics and phylogenetic inferences indicated that (1) ammonium-utilizing bacteria might form consortia to alleviate or avoid the negative influence of high ammonium concentration on other microorganisms, and (2) members of the Crenarchaeota found in the sediment might be involved in ammonium oxidation. This study is the first to report the composition of the microbial assemblages and phylogenetic characteristics of prokaryotic populations extant in leachate sediment. Additional work on microbial activity and contaminant biodegradation remains to be explored.     

Impacts of microbial community composition on isotope fractionation during reductive dechlorination of tetrachloroethylene

Isotope fractionation has been used with increasing frequency as a tool to quantify degradation of chlorinated aliphatic pollutants in the environment. The objective of this research was to determine if the electron donor present in enrichment cultures prepared from uncontaminated sediments influenced the extent of isotope fractionation of tetrachloroethylene (PCE), either directly, or through its influence on microbial community composition. Two PCE-degrading enrichment cultures were prepared from Duck Pond (DP) sediment and were incubated with formate (DPF) or H₂ (DPH) as electron donor. DPF and DPH were significantly different in both product distribution and extent of isotope fractionation. Chemical and isotope analyses indicated that electron donors did not directly affect the product distribution or the extent of isotope fractionation for PCE reductive dechlorination. Instead, restriction fragment length polymorphism (RFLP) and sequence analysis of the 16S rRNA clone libraries of DPF and DPH identified distinct microbial communities in each enrichment culture, suggesting that differences in microbial communities were responsible for distinct product distributions and isotope fractionation between the two cultures. A dominant species identified only in DPH was closely related to known dehalogenating species (Sulfurospirillum multivorans and Sulfurospirillum halorespirans) and may be responsible for PCE degradation in DPH. Our study suggests that different dechlorinators exist at the same site and can be preferentially stimulated by different electron donors, especially over the long-term (i.e., years), typical of in-situ ground water remediation.     

Comparison of intact polar lipid with microbial community composition of vent deposits of the Rainbow and Lucky Strike hydrothermal fields

The intact polar lipid (IPL) composition of twelve hydrothermal vent deposits from the Rainbow (RHF) and Lucky Strike hydrothermal fields (LSHF) has been investigated in order to assess its utility as a proxy for microbial community composition associated with deep‐sea hydrothermal locations. Gene‐based culture‐independent surveys of the microbial populations of the same vent deposits have shown that microbial populations are different in the two locations and appear to be controlled by the geochemical and geological processes that drive hydrothermal circulation. Large differences in the IPL composition between these two sites are evident. In the ultramafic‐hosted RHF, mainly archaeal‐IPLs were identified, including those known to be produced by hyperthermophilic Euryarchaeota. More specifically, polyglycosyl derivatives of archaeol and macrocyclic archaeol indicate the presence of hyperthermophilic methanogenic archaea in the vent deposits, which are related to members of the Methanocaldococcaceae or Methanococcaceae. In contrast, bacterial IPLs dominate IPL distributions from LSHF, suggesting that bacteria are more predominant at LSHF than at RHF. Bacterial Diacyl glycerol (DAG) IPLs containing phosphocholine, phosphoethanolamine or phosphoglycerol head groups were identified at both vent fields. In some vent deposits from LSHF ornithine lipids and IPLs containing phosphoaminopentanetetrol head groups were also observed. By comparison with previously characterized bacterial communities at the sites, it is likely the DAG‐IPLs observed derive from Epsilon‐ and Gammaproteobacteria. Variation in the relative amounts of archaeal versus bacterial IPLs appears to indicate differences in the microbial community between vent sites. Overall, IPL distributions appear to be consistent with gene‐based surveys.     

In situ visualization of newly synthesized proteins in environmental microbes using amino acid tagging and click chemistry

Here we describe the application of a new click chemistry method for fluorescent tracking of protein synthesis in individual microorganisms within environmental samples. This technique, termed bioorthogonal non‐canonical amino acid tagging (BONCAT), is based on the in vivo incorporation of the non‐canonical amino acid L‐azidohomoalanine (AHA), a surrogate for l ‐methionine, followed by fluorescent labelling of AHA‐containing cellular proteins by azide‐alkyne click chemistry. BONCAT was evaluated with a range of phylogenetically and physiologically diverse archaeal and bacterial pure cultures and enrichments, and used to visualize translationally active cells within complex environmental samples including an oral biofilm, freshwater and anoxic sediment. We also developed combined assays that couple BONCAT with ribosomal RNA (rRNA)‐targeted fluorescence in situ hybridization (FISH), enabling a direct link between taxonomic identity and translational activity. Using a methanotrophic enrichment culture incubated under different conditions, we demonstrate the potential of BONCAT‐FISH to study microbial physiology in situ. A direct comparison of anabolic activity using BONCAT and stable isotope labelling by nano‐scale secondary ion mass spectrometry (¹⁵NH₃ assimilation) for individual cells within a sediment‐sourced enrichment culture showed concordance between AHA‐positive cells and ¹⁵N enrichment. BONCAT‐FISH offers a fast, inexpensive and straightforward fluorescence microscopy method for studying the in situ activity of environmental microbes on a single‐cell level.     

Temperature-dependent differences in community structure of bacteria involved in degradation of petroleum hydrocarbons under sulfate-reducing conditions

Aim: The aim of this study was to characterize the microbial community involved in anaerobic degradation of petroleum hydrocarbon under low‐ and moderate‐temperature conditions. Methods and Results: Sulfate‐reducing enrichment cultures growing on crude oil and p‐xylene were established at low and moderate temperatures. Bacterial community structures of the cultures were characterized by 16S rRNA gene‐based analysis and organisms responsible for degradation of p‐xylene were investigated by analysis of the bamA gene, involved in anaerobic degradation of aromatic compounds. The PCR‐denaturing gradient gel electrophoresis analysis indicated significant differences in microbial community structures among the cultures, depending on the temperatures of incubation. Difference depending on the temperatures was also observed in the cloning analysis of the bamA gene performed on the p‐xylene‐degrading enrichment cultures. Majority of clones detected in the culture of moderate temperature were related to Desulfosarcina ovata, whereas more diverse bamA gene sequences were obtained from the culture incubated at low temperature. Conclusions: Temperature‐dependent differences in microbial community were demonstrated by the analyses of two genes. It was suggested that sulfate‐reducing bacteria of phylogenetically different groups might be involved in the degradation of petroleum hydrocarbons in different temperature environments. Significance and Impact of the Study: This study is the first report of p‐xylene‐degrading sulfate‐reducing enrichment culture at low temperature. The results of the experiments at low temperature were distinctly different from those reported in previous studies performed at moderate temperatures.     

Profile of Microbial Community Structure and Presence of Endolithic Microorganisms Inside a Deep-Sea Rock

Microbial community structure in the depth profile of a deep-sea sedimentary rock collected from the Sanriku Escarpment in the Japan Trench at a depth of 6337 m were analyzed using enrichment culture methods and culture-independent molecular phylo-genetic techniques. The rock was subsampled at four depths (S1 to S4; from the surface to the inside), and carbon concentrations and colony-forming units (CFU) were determined under several culture conditions. Terminal-restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified 16S rRNA gene (rDNA) sequences indicated that a shift in bacterial and archaeal ribotype structures occurred in the sections at different depths from the surface. rDNA clone analysis revealed a significant change in microbial rDNA community structure. Bacterial community rDNA in sections S1 to S3 consisted of typical marine bacteria mainly members of the f and n -subclass of Proteobacteria, while the inner most section, S4, contained rDNA signatures for the g -subclass of Proteobacteria and the High G + C Gram-Positive Group. Major archaeal rDNA clones shifted from Marine Group I (S1) to Thermococcales (S2-S4). The changes in bacterial and archaeal rDNA community structure indicated the possible infiltration of seawater and microorganisms into the rock and strongly suggested the isolation of endolithic microbial communities over the geological history of the rock.     

Boosting mediated electron transfer in bioelectrochemical systems with tailored defined microbial cocultures

Bioelectrochemical systems (BES) hold great promise for sustainable energy generation via a microbial catalyst from organic matter, for example, from wastewater. To improve current generation in BES, understanding the underlying microbiology of the electrode community is essential. Electron mediator producing microorganism like Pseudomonas aeruginosa play an essential role in efficient electricity generation in BES. These microbes enable even nonelectroactive microorganism like Enterobacter aerogenes to contribute to current production. Together they form a synergistic coculture, where both contribute to community welfare. To use microbial co‐operation in BES, the physical and chemical environments provided in the natural habitats of the coculture play a crucial role. Here, we show that synergistic effects in defined cocultures of P. aeruginosa and E. aerogenes can be strongly enhanced toward high current production by adapting process parameters, like pH, temperature, oxygen demand, and substrate requirements. Especially, oxygen was identified as a major factor influencing coculture behavior and optimization of its supply could enhance electric current production over 400%. Furthermore, operating the coculture in fed‐batch mode enabled us to obtain very high current densities and to harvest electrical energy for 1 month. In this optimized condition, the coulombic efficiency of the process was boosted to 20%, which is outstanding for mediator‐based electron transfer. This study lays the foundation for a rationally designed utilization of cocultures in BES for bioenergy generation from specific wastewaters or for bioprocess sensing and for benefiting from their synergistic effects under controlled bioprocess condition.     

Effects of electron donors on anaerobic microbial debromination of polybrominated diphenyl ethers (PBDEs)

Polybrominated diphenyl ethers (PBDEs) are a class of widely used flame retardants that have been highly accumulated in sediments. It is reported that microorganisms play an important role in the reductive debromination of PBDEs in anaerobic sediments. However, little is known about the effects of electron donors on the microbial community structure and their debromination capacity in PBDE transformation. In this study, alternate carbon substrates were used as electron donors to enrich the PBDE-debrominating microbial consortia to evaluate the effects of electron donors on PBDE microbial debromination. Decabromodiphenyl ether (BDE-209) was found to be the dominant (more than 50%) PBDEs congener in all consortia, and the percentage of BDE-209 was deceased by 12% (methanol), 11% (ethanol), 8% (acetate), 9% (lactate), 5% (pyruvate), and 11% (no electron donors), while the relative abundances of most lesser-brominated PBDEs increased after 90-day incubation compared to the initial profile of PBDEs. Substantial shifts in the microbial community structure among different amendments were observed based on denaturing gradient gel electrophoresis results. Pseudomonas spp. were identified to be the predominant organisms and the abundances of Band R, which was associated with Pseudomonas sp. SCSWA09, was well correlated with the biodegradation rate of BDE-209. Finally, the microbial community structure was highly correlated with the concentration of deca-BDE, octa-BDE and total nitrogen. These results provide insights into in situ bioremediation of environments contaminated by PBDEs and our understanding of microbial ecology associated with PBDE-debromination.     

Resuscitation of viable but non‐culturable bacteria to enhance the cellulose‐degrading capability of bacterial community in composting

Nowadays, much of what we know regarding the isolated cellulolytic bacteria comes from the conventional plate separation techniques. However, the culturability of many bacterial species is controlled by resuscitation‐promoting factors (Rpfs) due to entering a viable but non‐culturable (VBNC) state. Therefore, in this study, Rpf from Micrococcus luteus was added in the culture medium to evaluate its role in bacterial isolation and enhanced effects on cellulose‐degrading capability of bacterial community in the compost. It was found that Proteobacteria and Actinobacteria were two main phyla in the compost sample. The introduction of Rpf could isolate some unique bacterial species. The cellulase activity of enrichment cultures with and without Rpf treatment revealed that Rpf treatment significantly enhanced cellulase activity. Ten isolates unique in Rpf addition displayed carboxymethyl‐cellulase (CMCase) activity, while six isolates possessed filter paper cellulase (FPCase) activity. This study provides new insights into broader cellulose degraders, which could be utilized for enhancing cellulosic waste treatment.     

The putative functional ecology and distribution of archaeal communities in sponges,sediment and seawater in a coral reef environment

Archaea play crucial roles in a number of key ecological processes including nitrification and methanogenesis. Although several studies have been conducted on these organisms, the roles and dynamics of coral reef archaeal communities are still poorly understood, particularly in host and nonhost biotopes and in high (HMA) and low microbial abundance (LMA) sponges. Here, archaeal communities detected in six distinct biotopes, namely, sediment, seawater and four different sponge species Stylissa carteri, Stylissa massa, Xestospongia testudinaria and Hyrtios erectus from the Spermonde Archipelago, SW Sulawesi, Indonesia were investigated using 454‐pyrosequencing of 16S rRNA genes (OTU cut‐off 97%). Archaeal communities from sediment and sponges were dominated by Crenarchaeota, while the seawater community was dominated by Euryarchaeota. The biotope explained almost 75% of the variation in archaeal composition, with clear separation between microbial assemblages from sediment, X. testudinaria and H. erectus (HMA). In contrast, samples from seawater and both Stylissa species (LMA) showed considerable overlap in the ordination and, furthermore, shared most abundant OTUs with the exception of a single dominant OTU specifically enriched in both Stylissa species. Predicted functional gene content in archaeal assemblages also revealed significant differences among biotopes. Different ammonia assimilation strategies were exhibited by the archaeal communities: X. testudinaria, H. erectus and sediment archaeal communities were enriched for glutamate dehydrogenase with mixed specificity (NAD(P)⁺) pathways, while archaeal planktonic communities were enriched for specific glutamate dehydrogenase (NADP⁺) and glutamate synthase pathways. Archaeal communities in Stylissa had intermediate levels of enrichment. Our results indicate that archaeal communities in different biotopes have distinct ecophysiological roles.     

海南东寨港红树林不同植被土壤微生物群落结构比较

【目的】比较不同植被下红树林土壤细菌和古菌的多样性及群落结构,认识红树林土壤微生物资源多样性。【方法】直接提取红树林土壤总DNA,采用细菌通用引物27F/1492R和古菌通用引物Arch21F/Arch958R进行PCR扩增,构建细菌和古菌16S rRNA基因文库,对海南东寨港自然保护区秋茄林、无瓣海桑林和无红树林裸滩土壤的细菌和古菌多样性和群落结构进行分析和比较。【结果】3种土壤样品的细菌类群包括变形细菌门(Proteobacteria)等16个类群,其中变形细菌门(Proteobacteria)与绿屈挠菌门(Chloroflexi)是优势类群;古菌包括6个嗜泉古菌界(Crenarchaeota)类群和7个广域古菌界(Euryarchaeota)类群,分别以Marine Benthic Group C、Marine Benthic Group D为优势类群。多样性指数(H’)和物种丰富度指数(Schao1)表明,本地种秋茄林下土壤细菌和古菌的多样性指数最高,外来种无瓣海桑显著低于秋茄林,甚至明显低于相邻无红树林裸滩沉积物;不同植被下土壤细菌和古菌群落结构存在显著差异,秋茄林土壤微生物群落结构和无红树林裸滩沉积物更相似。【结论】红树林土壤微生物类群丰富,不同植被下土壤细菌和古菌多样性和群落结构存在显著差异。     

Respiratory interactions of soil bacteria with (semi)conductive iron‐oxide minerals

Pure‐culture studies have shown that dissimilatory metal‐reducing bacteria are able to utilize iron‐oxide nanoparticles as electron conduits for reducing distant terminal acceptors; however, the ecological relevance of such energy metabolism is poorly understood. Here, soil microbial communities were grown in electrochemical cells with acetate as the electron donor and electrodes (poised at 0.2 V versus Ag/AgCl) as the electron acceptors in the presence and absence of iron‐oxide nanoparticles, and respiratory current generation and community structures were analysed. Irrespective of the iron‐oxide species (hematite, magnetite or ferrihydrite), the supplementation with iron‐oxide minerals resulted in large increases (over 30‐fold) in current, while only a moderate increase (～10‐fold) was observed in the presence of soluble ferric/ferrous irons. During the current generation, insulative ferrihydrite was transformed into semiconductive goethite. Clone‐library analyses of 16S rRNA gene fragments PCR‐amplified from the soil microbial communities revealed that iron‐oxide supplementation facilitated the occurrence of Geobacter species affiliated with subsurface clades 1 and 2. We suggest that subsurface‐clade Geobacter species preferentially thrive in soil by utilizing (semi)conductive iron oxides for their respiration.     

Response of 1,2-dichloroethane-adapted microbial communities to ex-situ biostimulation of polluted groundwater

The microbial community of a groundwater system contaminated by 1,2-dichloroethane (1,2-DCA), a toxic and persistent chlorinated hydrocarbon, has been investigated for its response to biostimulation finalized to 1,2-DCA removal by reductive dehalogenation. The microbial population profile of samples from different wells in the aquifer and from microcosms enriched in the laboratory with different organic electron donors was analyzed by ARISA (Amplified Ribosomal Intergenic Spacer Analysis) and DGGE (Denaturing Gradient Gel Electrophoresis) of 16S rRNA genes. 1,2-DCA was completely removed with release of ethene from most of the microcosms supplemented with lactate, acetate plus formate, while cheese whey supported 1,2-DCA dehalogenation only after a lag period. Microbial species richness deduced from ARISA profiles of the microbial community before and after electron donor amendments indicated that the response of the community to biostimulation was heterogeneous and depended on the well from which groundwater was sampled. Sequencing of 16S rRNA genes separated by DGGE indicated the presence of bacteria previously associated with soils and groundwater polluted by halogenated hydrocarbons or present in consortia active in the removal of these compounds. A PCR assay specific for Desulfitobacterium sp. showed the enrichment of this genus in some of the microcosms. The dehalogenation potential of the microbial community was confirmed by the amplification of dehalogenase-related sequences from the most active microcosms. Cloning and sequencing of PCR products indicated the presence in the metagenome of the bacterial community of a new dehalogenase potentially involved in 1,2-DCA reductive dechlorination.     

Influence of Hydraulic Retention Time on Extent of PCE Dechlorination and Preliminary Characterization of the Enrichment Culture

The extent of tetrachloroethene (PCE) dechlorination in two chemostats was evaluated as a function of hydraulic retention time (HRT). The inoculum of these chemostats was from an upflow anaerobic sludge blanket (UASB) reactor that rapidly converts PCE to vinyl chloride (VC) and ethene. When the HRT was 2.9 days, PCE was converted only to cis-dichloroethene (cDCE). When the HRT was 11 days, the end products were VC and ethene. Further studies showed that the dechlorinating microbial community in the UASB reactor contained two distinct populations, one of which converted PCE to cDCE and the other cDCE to VC and ethene. Methanogenic activity was very low in these cultures. The cDCE dechlorinating culture apparently has a lower growth rate than the PCE dechlorinating culture, and as a result, at a shorter HRT, the cDCE dechlorinating culture was washed out from the system leading to incomplete dechlorination of PCE. Both enrichment cultures used pyruvate or hydrogen as electron donors for dechlorination. Acetate was the carbon source (but not energy source) when hydrogen was used. Both cultures had undefined nutrient requirements and needed supplements of cell extract obtained from the mixed culture in the UASB reactor. However, the two cultures were different in their response to the addition of an inhibitor of methanogenesis (2-bromoethanesulfonate [BES]). BES inhibited the dechlorinating activity of the enriched cDCE dechlorinating culture, but had no influence on the PCE dechlorinating culture. Preliminary studies on BES inhibition are presented.     

Characterisation of culture-independent and -dependent microbial communities in a high-temperature offshore chalk petroleum reservoir

Recent studies have indicated that oil reservoirs harbour diverse microbial communities. Culture-dependent and culture-independent methods were used to evaluate the microbial diversity in produced water samples of the Ekofisk oil field, a high temperature, and fractured chalk reservoir in the North Sea. DGGE analyses of 16S rRNA gene fragments were used to assess the microbial diversity of both archaeal and bacterial communities in produced water samples and enrichment cultures from 4 different wells (B-08, X-08, X-18 and X-25). Low diversity communities were found when 16S rDNA libraries of bacterial and archaeal assemblages were generated from total community DNA obtained from produced water samples and enrichment cultures. Sequence analysis of the clones indicated close matches to microbes associated with high-temperature oil reservoirs or other similar environments. Sequences were found to be similar to members of the genera Thermotoga, Caminicella, Thermoanaerobacter, Archaeoglobus, Thermococcus, and Methanobulbus. Enrichment cultures obtained from the produced water samples were dominated by sheathed rods. Sequence analyses of the cultures indicated predominance of the genera Petrotoga, Arcobacter, Archaeoglobus and Thermococcus. The communities of both produced water and enrichment cultures appeared to be dominated by thermophilic fermenters capable of reducing sulphur compounds. These results suggest that the biochemical processes in the Ekofisk chalk reservoir are similar to those observed in high-temperature sandstone reservoirs.