Aerobic Cometabolism of Chloroform and 1,1,1-Trichloroethane by Butane-Grown Microorganisms

Aerobic cometabolism of chloroform (CF) and 1,1,1-trichloroethane (1,1,1-TCA) was observed by subsurface microorganisms grown on butane. Studies performed in batch incubated microcosms were screened for CF transformation potential using the following cometabolic substrates: ammonia, methane, propane, butane, propene, octane, isoprene, and phenol. CF transformation was observed in microcosms fed ammonia, methane, propane, and butane. The butane microcosms achieved the most effective transformation. The transformation of CF and 1,1,1-TCA was strongly correlated with butane utilization and oxygen consumption. CF transformation ceased in the absence of butane or when oxygen was depleted to low concentrations in the microcosms. No transformation of carbon tetrachloride was observed. With successive additions of CF and butane to the microcosms, complete transformation of CF was achieved at solution concentrations as high as 1 mg/L. High CF concentrations appeared to inhibit butane utilization. Maximum transformation yield (T_y) of 0.01 mg CF trans-formed/mg of butane consumed, were achieved. The results indicate that a monooxygenase enzyme required for butane utilization is likely responsible for the transformation of CF. Chloride measurements demonstrated that CF was completely dechlorinated. Approximately 70% of the chloride in the transformed 1,1,1 -TCA was released into solution, indicating incomplete dechlorination of 1,1,1-TCA. The results indicate that butane is a promising cometabolic substrate for the transformation of chlorinated methanes, chlorinated ethanes, and potentially chlorinated ethenes.     

Comparison of TCE Transformation Abilities of Methane- and Propane-Utilizing Microorganisms

Subsurface microorganisms from McClellan Air Force Base (AFB) were grown in batch aquifer microcosms on methane, propane, and butane to evaluate the potential for aerobic trichloroethylene (TCE) cometabolism. Microorganisms stimulated on all three substrates indicated the existence of a subsurface microbial community capable of utilizing alkanes as growth substrates. Initial growth substrate utilization lag periods of 2 weeks for methane and 3 weeks for propane and butane were observed. Methane- and propane-utilizers were active toward TCE cometabolism, whereas butane-utilizers showed no ability to transform TCE. Gradually increasing TCE concentrations were effectively transformed with uniform additions of methane and propane for up to 1 year. TCE was transformed most rapidly during active methane utilization, and continued at a slower rate for approximately 1 week after methane was consumed. Propane microcosms maintained first-order TCE transformation for up to 4 weeks after propane was consumed. The microbial communities remained active toward primary substrate utilization as the TCE concentration was gradually increased. Both methane- and propane-utilizers showed positive correlations between TCE transformation rates and primary substrate utilization rates. Observed maximum TCE transformation yields were 0.068 g TCE/g methane and 0.048 g TCE/g propane. The methane-utilizers also transformed chloroform (CF) but not 1,1,1-trichloroethane (1,1,1-TCA). Propane-utilizers transformed both CF and 1,1,1-TCA, indicating they were better suited for cometabolizing chlorinated aliphatic hydrocarbon mixtures in the McClellan AFB subsurface.     

A 1,1,1-trichloroethane-degrading anaerobic mixed microbial culture enhances biotransformation of mixtures of chlorinated ethenes and ethanes

1,1,1-trichloroethane (1,1,1-TCA) is a common groundwater pollutant as a result of improper disposal and accidental spills. It is often found as a cocontaminant with trichloroethene (TCE) and inhibits some TCE-degrading microorganisms. 1,1,1-TCA removal is therefore required for effective bioremediation of sites contaminated with mixed chlorinated organics. This study characterized MS, a 1,1,1-TCA-degrading, anaerobic, mixed microbial culture derived from a 1,1,1-TCA-contaminated site in the northeastern United States. MS reductively dechlorinated 1,1,1-TCA to 1,1-dichloroethane (1,1-DCA) and then to monochloroethane (CA) but not further. Cloning of bacterial 16S rRNA genes revealed among other organisms the presence of a Dehalobacter sp. and a Desulfovibrio sp., which are both phylogenetically related to known dehalorespiring strains. Monitoring of these populations with species-specific quantitative PCR during degradation of 1,1,1-TCA and 1,1-DCA showed that Dehalobacter proliferated during dechlorination. Dehalobacter growth was dechlorination dependent, whereas Desulfovibrio growth was dechlorination independent. Experiments were also performed to test whether MS could enhance TCE degradation in the presence of inhibiting levels of 1,1,1-TCA. Dechlorination of cis-dichloroethene (cDCE) and vinyl chloride (VC) in KB-1, a chloroethene-degrading culture used for bioaugmentation, was inhibited with 1,1,1-TCA present. When KB-1 and MS were coinoculated, degradation of cDCE and VC to ethene proceeded as soon as the 1,1,1-TCA was dechlorinated to 1,1-DCA by MS. This demonstrated the potential application of the MS and KB-1 cultures for cobioaugmentation of sites cocontaminated with 1,1,1-TCA and TCE.     

A 1,1,1-Trichloroethane-Degrading Anaerobic Mixed Microbial Culture Enhances Biotransformation of Mixtures of Chlorinated Ethenes and Ethanes

1,1,1-Trichloroethane (1,1,1-TCA) is a common groundwater pollutant as a result of improper disposal and accidental spills. It is often found as a cocontaminant with trichloroethene (TCE) and inhibits some TCE-degrading microorganisms. 1,1,1-TCA removal is therefore required for effective bioremediation of sites contaminated with mixed chlorinated organics. This study characterized MS, a 1,1,1-TCA-degrading, anaerobic, mixed microbial culture derived from a 1,1,1-TCA-contaminated site in the northeastern United States. MS reductively dechlorinated 1,1,1-TCA to 1,1-dichloroethane (1,1-DCA) and then to monochloroethane (CA) but not further. Cloning of bacterial 16S rRNA genes revealed among other organisms the presence of a Dehalobacter sp. and a Desulfovibrio sp., which are both phylogenetically related to known dehalorespiring strains. Monitoring of these populations with species-specific quantitative PCR during degradation of 1,1,1-TCA and 1,1-DCA showed that Dehalobacter proliferated during dechlorination. Dehalobacter growth was dechlorination dependent, whereas Desulfovibrio growth was dechlorination independent. Experiments were also performed to test whether MS could enhance TCE degradation in the presence of inhibiting levels of 1,1,1-TCA. Dechlorination of cis-dichloroethene (cDCE) and vinyl chloride (VC) in KB-1, a chloroethene-degrading culture used for bioaugmentation, was inhibited with 1,1,1-TCA present. When KB-1 and MS were coinoculated, degradation of cDCE and VC to ethene proceeded as soon as the 1,1,1-TCA was dechlorinated to 1,1-DCA by MS. This demonstrated the potential application of the MS and KB-1 cultures for cobioaugmentation of sites cocontaminated with 1,1,1-TCA and TCE.     

Kinetic and inhibition studies for the aerobic cometabolism of 1,1,1-trichloroethane, 1,1-dichloroethylene,and 1,1-dichloroethane by a butane-grown mixed culture

Batch kinetic and inhibition studies were performed for the aerobic cometabolism of 1,1,1-trichloroethane (1,1,1-TCA), 1,1-dichloroethylene (1,1-DCE), and 1,1-dichloroethane (1,1-DCA) by a butane-grown mixed culture. These chlorinated aliphatic hydrocarbons (CAHs) are often found together as cocontaminants in groundwater. The maximum degradation rates (k(max)) and half-saturation coefficients (K(s)) were determined in single compound kinetic tests. The highest k(max) was obtained for butane (2.6 micromol/mg TSS/h) followed by 1,1-DCE (1.3 micromol/mg TSS/h), 1,1-DCA (0.49 micromol/mg TSS/h), and 1,1,1-TCA (0.19 micromol/mg TSS/h), while the order of K(s) from the highest to lowest was 1,1-DCA (19 microM), butane (19 microM), 1,1,1-TCA (12 microM) and 1,1-DCE (1.5 microM). The inhibition types were determined using direct linear plots, while inhibition coefficients (K(ic) and K(iu)) were estimated by nonlinear least squares regression (NLSR) fits to the kinetic model of the identified inhibition type. Two different inhibition types were observed among the compounds. Competitive inhibition among CAHs was indicated from direct linear plots, and the CAHs also competitively inhibited butane utilization. 1,1-DCE was a stronger inhibitor than the other CAHs. Mixed inhibition of 1,1,1-TCA, 1,1-DCA, and 1,1-DCE transformations by butane was observed. Thus, both competitive and mixed inhibitions are important in cometabolism of CAHs by this butane culture. For competitive inhibition between CAHs, the ratio of the K(s) values was a reasonable indicator of competitive inhibition observed. Butane was a strong inhibitor of CAH transformation, having a much lower inhibition coefficient than the K(s) value of butane, while the CAHs were weak inhibitors of butane utilization. Model simulations of reactor systems where both the growth substrate and the CAHs are present indicate that reactor performance is significantly affected by inhibition type and inhibition coefficients. Thus, determining inhibition type and measuring inhibition coefficients is important in designing CAH treatment systems.     

Microcosm and in situ field studies of enhanced biotransformation of trichloroethylene by phenol-utilizing microorganisms.

The ability of different aerobic groundwater microorganisms to cometabolically degrade trichloroethylene (TCE), 1,2-cis-dichloroethylene (c-DCE), and 1,2-trans-dichloroethylene (t-DCE) was evaluated both in groundwater-fed microcosms and in situ in a shallow aquifer. Microcosms amended with phenol or toulene were equally effective in removing c-DCE (> 90%) followed by TCE (60 to 70%), while the microcosm fed methane was most effective in removing t-DCE (> 90%). The microcosm fed ammonia was the least effective. None of the microcosms effectively degraded 1,1,1-trichloroethane. At the Moffett Field groundwater test site, in situ removal of c-DCE and TCE coincided with biostimulation through phenol and oxygen injection and utilization, with c-DCE removed more rapidly than TCE. Greater TCE and c-DCE removal was observed when the phenol concentration was increased. Over 90% removal of c-DCE and TCE was observed in the 2-m biostimulated zone. This compares with 40 to 50% removal of c-DCE and 15 to 25% removal of TCE achieved by methane-grown microorganisms previously evaluated in an adjacent in situ test zone. The in situ removal with phenol-grown microorganisms agrees qualitatively with the microcosm studies, with the rates and extents of removal ranked as follows: c-DCE > TCE > t-DCE. These studies demonstrate the potential for in situ TCE bioremediation using microorganisms grown on phenol.     

Anaerobic Bioremediation of Groundwater Containing a Mixture of 1,1,2,2-Tetrachloroethane and Chloroethenes

This study investigated the biotransformation pathways of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) in the presence of chloroethenes (i.e. tetrachloroethene, PCE; trichloroethene, TCE) in anaerobic microcosms constructed with subsurface soil and groundwater from a contaminated site. When amended with yeast extract, lactate, butyrate, or H₂ and acetate, 1,1,2,2-TeCA was initially dechlorinated via both hydrogenolysis to 1,1,2-trichloroethane (1,1,2-TCA) (major pathway) and dichloroelimination to dichloroethenes (DCEs) (minor pathway), with both reactions occurring under sulfidogenic conditions. In the presence of only H₂, the hydrogenolysis of 1,1,2,2-TeCA to 1,1,2-TCA apparently required the presence of acetate to occur. Once formed, 1,1,2-TCA was degraded predominantly via dichloroelimination to vinyl chloride (VC). Ultimately, chloroethanes were converted to chloroethenes (mainly VC and DCEs) which persisted in the microcosms for very long periods along with PCE and TCE originally present in the groundwater. Hydrogenolysis of chloroethenes occurred only after highly reducing methanogenic conditions were established. However, substantial conversion to ethene (ETH) was observed only in microcosms amended with yeast extract (200 mg/l), suggesting that groundwater lacked some nutritional factors which were likely provided to dechlorinating microorganisms by this complex organic substrate. Bioaugmentation with an H₂-utilizing PCE-dechlorinating Dehalococcoides spp. -containing culture resulted in the conversion of 1,1,2,2-TeCA, PCE and TCE to ETH and VC. No chloroethanes accumulated during degradation suggesting that 1,1,2,2-TeCA was degraded through initial dichloroelimination into DCEs and then typical hydrogenolysis into ETH and VC.     

A combined method for determining inhibition type, kinetic parameters, and inhibition coefficients for aerobic cometabolism of 1,1,1-trichloroethane by a butane-grown mixed culture.

A combined method for determining inhibition type, kinetic parameters, and inhibition coefficients is developed and presented. The method was validated by applying it to data obtained from batch kinetics of the aerobic cometabolism of 1,1,1-trichloroethane (1,1,1-TCA) by a butane-grown mixed culture. The maximum degradation rates (k(max)) and half-saturation coefficients (K(s)) were independently determined in single compound tests, and compared with those obtained from inhibition tests. The inhibition type was determined using direct linear plots at various substrate and inhibitor concentrations. Kinetic parameters (k(max) and K(s)) and inhibition coefficients (K(ic) and K(iu)) were determined by nonlinear least squares regression (NLSR) fits of the inhibition model determined from the direct linear plots. Initial guesses of the kinetic parameters for NLSR were determined from linearized inhibition equations that were derived from the correlations between apparent maximum degradation rates (k(app)(max)) and/or the apparent half-saturation coefficient (K(app)(s)) and the k(max), K(s), and inhibitor concentration (I(L)) for each inhibition equation. Two different inhibition types were indicated from the direct linear plots: competitive inhibition of 1,1,1-TCA on butane degradation, and mixed inhibition of 1,1,1-TCA transformation by butane. Good agreement was achieved between independently measured k(max) and K(s) values and those obtained from both NLSR and the linearized inhibition equations. The initial guesses of all the kinetic parameters determined from linear plots were in the range of the values estimated from NLSR analysis. Overall the results show that use of the direct linear plot method to identify the inhibition type, coupled with initial guesses from linearized plots for NLSR analysis, results in an accurate method for determining inhibition types and coefficients. Detailed studies with pure cultures and purified enzymes are needed to further demonstrate the utility of this method.     

Impacts of gene bioaugmentation with pJP4-harboring bacteria of 2,4-D-contaminated soil slurry on the indigenous microbial community

Gene bioaugmentation is a bioremediation strategy that enhances biodegradative potential via dissemination of degradative genes from introduced microorganisms to indigenous microorganisms. Bioremediation experiments using 2,4-dichlorophenoxyacetic acid (2,4-D)-contaminated soil slurry and strains of Pseudomonas putida or Escherichia coli harboring a self-transmissible 2,4-D degradative plasmid pJP4 were conducted in microcosms to assess possible effects of gene bioaugmentation on the overall microbial community structure and ecological functions (carbon source utilization and nitrogen transformation potentials). Although exogenous bacteria decreased rapidly, 2,4-D degradation was stimulated in bioaugmented microcosms, possibly because of the occurrence of transconjugants by the transfer of pJP4. Terminal restriction fragment length polymorphism analysis revealed that, although the bacterial community structure was disturbed immediately after introducing exogenous bacteria to the inoculated microcosms, it gradually approached that of the uninoculated microcosms. Biolog assay, nitrate reduction assay, and monitoring of the amoA gene of ammonia-oxidizing bacteria and nirK and nirS genes of denitrifying bacteria showed no irretrievable depressive effects of gene bioaugmentation on the carbon source utilization and nitrogen transformation potentials. These results may suggest that gene bioaugmentation with P. putida and E. coli strains harboring pJP4 is effective for the degradation of 2,4-D in soil without large impacts on the indigenous microbial community.     

三氯乙烷污染地地下水中Dehalobacter属细菌定量与多样性分析

[目的]对某公司6个以1,1,1-三氯乙烷(1,1,1-Trichloroethane,1,1,1-TCA)为主要污染物的地下水样品中的降解微生物Dehalobacter spp.(Dhb)进行相对定量和多样性分析.[方法]采用气相色谱法测定6个样品中1,1,1-TCA、1,1-二氯乙烷(1,1-DCA)和氯乙烷(CA)的浓度;通过定量PCR法分别测定6个样品中Dhb占总菌的百分比;以16S rRNA基因通用引物和Dhb特异性引物扩增获得的PCR产物构建了6个样品的Dhb特异性克隆文库,所得序列与GenBank中的最相似序列构建系统发育树.[结果]6个样品中均有1,1-DCA和(或)CA的检出,推测此6处地下水中1,1,1-TCA可能存在生物降解.定量PCR结果表明,6个样品中Dhb丰度差异较大.6个Dhb特异性克隆文库获得41条序列,序列比对结果表明,与它们最相似的已知分类地位的序列全部属于Dhb属.这些序列按99％的相似性被划分成7个可操作性分类单元(OTU).其中24条序列属于OTU1,该OTU的序列与已知能阵解1,1,1-TCA的Dehalobacter sp.str.TCA1的16S rRNA基因序列相似性达98％;文库中的3个OTU与GenBank中16S rRNA基因序列同源性最高仅为95％-96％.[结论]该污染场地地下水中存在多样性较丰富的降解微生物Dehalobacter属细菌,它们可能与现场的1,1,1-TCA生物降解有关.     

Tracking the Response of Burkholderia cepacia G4 5223-PR1 in Aquifer Microcosms

The introduction of bacteria into the environment for bioremediation purposes (bioaugmentation) requires analysis and monitoring of microbial population dynamics to define persistence and activity from both efficacy and risk assessment perspectives. Burkholderia cepacia G4 5223-PR1 is a Tn5 insertion mutant which constitutively expresses a toluene ortho-monooxygenase that degrades trichloroethylene (TCE). This ability of G4 5223-PR1 to degrade TCE without aromatic induction may be useful for bioremediation of TCE-containing aquifers and groundwater. Thus, a simulated aquifer sediment system and groundwater microcosms were used to monitor the survival of G4 5223-PR1. The fate of G4 5223-PR1 in sediment was monitored by indirect immunofluorescence microscopy, a colony blot assay, and growth on selective medium. G4 5223-PR1 was detected immunologically by using a highly specific monoclonal antibody which reacted against the O-specific polysaccharide chain of the lipopolysaccharides of this organism. G4 5223-PR1 survived well in sterilized groundwater, although in nonsterile groundwater microcosms rapid decreases in the G4 5223-PR1 cell population were observed. Ten days after inoculation no G4 5223-PR1 cells could be detected by selective plating or immunofluorescence. G4 5223-PR1 survival was greater in a nonsterile aquifer sediment microcosm, although after 22 days of elution the number of G4 5223-PR1 cells was low. Our results demonstrate the utility of monoclonal antibody tracking methods and the importance of biotic interactions in determining the persistence of introduced microorganisms.     

Effects of Introduced Groundwater on Water Chemistry and Fish Assemblages in Central Florida Lakes

We assessed effects of groundwater pumping to elevate lake levels on lake water chemistry and fish population metrics at seven Florida lakes. Following groundwater pumping, lake level fluctuation was reduced and lake water samples increased in mean pH, total alkalinity, total phosphorus, chloride and Secchi depth compared to historical means, indicating a close resemblance to the chemistry of aquifer water in the region. Fish community metrics from the augmented lakes were compared to 36 non-augmented lakes in Florida. The mean values for catch per unit effort, species richness and biomass of harvestable fishes, determined by electrofishing, were lower in augmented lakes compared to non-augmented lakes. Canonical correspondence analysis (CCA) indicated a high probability of a low abundance of individual species in augmented lakes compared to a majority of non-augmented lakes. The augmented lake with the lowest pumping rate exhibited less of a shift in limnological variables from historical values, and had fish population characteristics more closely resembling those of non-augmented lakes. Thus, reduced volumes of groundwater introduction could lower impacts to limnological and fish population characteristics. Augmentation allows for lakes to be utilized for recreational activities, and without augmentation some lakes in central Florida would likely go dry due to groundwater withdrawals for water supply. Therefore, allowing more natural water level fluctuations and possible reductions in total pumpage are recommended to reduce impacts to limnological and fish population characteristics, while still allowing sufficient groundwater pumping to preserve lake habitats.     

Molinate biodegradation in soils: natural attenuation versus bioaugmentation

The aims of the present study were to assess the potential of natural attenuation or bioaugmentation to reduce soil molinate contamination in paddy field soils and the impact of these bioremediation strategies on the composition of soil indigenous microbiota. A molinate mineralizing culture (mixed culture DC) was used as inoculum in the bioaugmentation assays. Significantly higher removal of molinate was observed in bioaugmentation than in natural attenuation microcosms (63 and 39 %, respectively) after 42 days of incubation at 22 °C. In the bioaugmentation assays, the impact of Gulosibacter molinativorax ON4^T on molinate depletion was observed since the gene encoding the enzyme responsible for the initial molinate breakdown (harboured by that actinobacterium) was only detected in inoculated microcosms. Nevertheless, the exogenous mixed culture DC did not overgrow as the heterotrophic counts of the bioaugmentation microcosms were not significantly different from those of natural attenuation and controls. Moreover, the actinobacterial clone libraries generated from the bioaugmentation microcosms did not include any 16S rRNA gene sequences with significant similarity to that of G. molinativorax ON4^T. The multivariate analysis of the 16S rRNA DGGE patterns of the soil microcosm suggested that the activity of mixed culture DC did not affect the soil bacterial community structure since the DGGE patterns of the bioaugmentation microcosms clustered with those of natural attenuation and controls. Although both bioremediation approaches removed molinate without indigenous microbiota perturbation, the results suggested that bioaugmentation with mixed culture DC was more effective to treat soils contaminated with molinate.     

Population dynamics in bioaugmented membrane bioreactor for treatment of bromoamine acid wastewater

The performances and microbial population changes in laboratory-scale membrane bioreactor (MBR) augmented with Sphingomonas xenophaga QYY were investigated in the present study. It was demonstrated that after 30 days acclimation, the non-augmented MBR system were able to degrade bromoamine acid (BAA) well. However, the efficiency of the system decreased with BAA concentration increasing. While the augmented MBR showed higher capability, in which the color and COD removal were more than 90% and 50%, respectively. By ribosomal intergenic spacer analysis (RISA), it was found that BAA-utilizing populations gradually increased to become the dominant species in the non-augmented MBR. However, the augmented MBR possessed relatively stable treatment abilities, in which the introduced strain QYY could be persistent and co-exist well with the indigenous populations.     

Rock Fragments in Trichloroethene Microcosms for Bedrock Aquifers

The purpose of this study was to evaluate microcosm methods that can be used to predict the in situ anaerobic reductive dechlorination of trichloroethene (TCE) in bedrock aquifers with and without amendments. Microcosm conditions (e.g., surface area:volume ratio, initial TCE concentration [C ₀], incubation temperature) were selected to simulate in situ conditions at the site. The effect of rock media in the microcosms as a source of surface area and nutrients was also assessed. Comparison was made between microcosms constructed with sterile rock media and rock media submerged for 45 days in a groundwater well within a TCE plume for field colonization. Statistically significant biotic degradation of TCE was observed in microcosms with both groundwater only and non-field-colonized rock media, when amended with lactate. Measured half-lives were similar to half-lives observed in field conditions. Normalizing biotic results to abiotic results provides a method that deducts the abiotic losses and allows complete comparison between sample rounds, assuming samples were randomly selected for analysis within the sample round to avoid systematic errors or variation.     

Anaerobic dechlorination of trichloroethene,tetrachloroethene and 1,2-dichloroethane by an acetogenic mixed culture in a fixed-bed reactor

An anaerobic enrichment culture with glucose as the sole source of carbon and energy plus trichloroethene (TCE) as a potential electron acceptor was inoculated with material from a full size anaerobic charcoal reactor that biologically eliminated dichloromethane from contaminated groundwater (Stromeyer et al. 1991). In subcultures of this enrichment complete sequential transformation of 10 µM TCE viacis-dichloroethene and chloroethene to ethene was reproducibly observed. Maintenance of this activity on subcultivation required the presence of TCE in the medium. The enrichment culture was used to inoculate an anaerobic fixed-bed reactor containing sintered glass Raschig elements as support material. The reactor had a total volume of 1780 ml and was operated at 20 °C in an up-flow mode with a flow rate of 50 ml/h. It was fed continuously with 2 mM glucose and 55 µM TCE. Glucose was converted to acetate as the major product and to a minor amount of methane; TCE was quantitatively dehalogenated to ethene. When, in addition to TCE, tetrachloroethene or 1,2-dichloroethane were added to the system, these compounds were also dehalogenated to ethene. In contrast, 1,1,1-trichloroethane was not dehalogenated, but at 40 µM severely inhibited acetogenesis and methanogenesis. When the concentration of TCE in the feed was raised to 220 µM, chloroethene transiently accumulated, but after an adaptation period ethene was again the only volatile product detected in the effluent. The volumetric degradation rate at this stage amounted to 6.2 µmol/l/h. Since complete transformation of TCE occurred in the first sixth of the reactor volume, the degradation capacity of the system is estimated to exceed this value by factor of about ten.Abbreviations CA chloroethane - 1,1-DCA 1,1-dichloroethane - 1,2-DCA 1,2-dichloroethane - 1,1-DCE 1,1-dichloroethene - c-DCE cis-1,2-dichloroethene - t-DCE trans-1,2-dichloroethene - PCE tetrachloroethene, perchloroethene - 1,1,1-TCA 1,1,1-trichloroethane - TCE trichloroethene - VC chloroethene, vinyl chloride     

The influence of microbial redox cycling on radionuclide mobility in the subsurface at a low-level radioactive waste storage site

As anaerobic microbial metabolism can have a major impact on radionuclide speciation and mobility in the subsurface, the solubility of uranium, technetium and radium was determined in microcosms prepared from sediments adjacent to the Drigg low-level radioactive waste storage site (UK). Both uranium (as U(VI);     ) and Tc (as Tc(VII);     ) were removed from groundwater concurrently with microbial Fe(III) reduction, presumably through reduction to insoluble U(IV) and Tc(IV), respectively, while Ra (Ra²⁺) that had rapidly sorbed onto mineral surfaces was not released following Fe(III) reduction. Biogenic Fe(II) minerals in reduced Drigg sediments were unable to reduce U(VI) abiotically but could reduce Tc(VII). Following addition of the oxidant nitrate to the reduced sediments, uranium was remobilized and released into solution, whereas technetium remained associated with an insoluble phase. A close relative of Pseudomonas stutzeri dominated the microbial communities under denitrifying conditions, reducing nitrate to nitrite in the microcosms, which was able to reoxidize Fe(II) and U(IV), with release of the latter into solution as U(VI). These data suggest that microbial Fe(III) reduction in the far-field at Drigg has the potential to decrease the migration of some radionuclides in the subsurface, and the potential for reoxidation and remobilization by nitrate, a common contaminant in nuclear waste streams, is radionuclide-specific.     

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.