六氯-1,3-丁二烯的微生物降解研究进展

六氯-1,3-丁二烯(hexachlorobutadiene,HCBD)是一种有毒有害的脂肪族氯代烃,曾经作为杀虫剂、除草剂、变压器油和传热流体等化学工业产品的重要成分被广泛应用于生产生活。HCBD因满足《关于持久性有机污染物的斯德哥尔摩公约》中风险筛选标准(如毒性、持久性、远距离环境迁移和生物累积性等),缔约方于2015年第七次会议中将其增列为持久性有机污染物,2017年又将其列入该公约的附件Ｃ以控制其环境排放量。目前关于HCBD的环境归趋仍是研究热点,但是对于HCBD的微生物降解转化机制尚缺乏深入研究。鉴于此,本文重点回顾并讨论了地下水、底泥等厌氧环境中已报道的HCBD微生物降解转化途径、速率及机制,并从热力学角度阐述HCBD及其降解产物作为电子受体通过还原性脱氯反应被厌氧脱卤微生物代谢转化的可行性。最后,本文根据现有研究结果,提出微生物厌氧降解HCBD的研究展望,包括多组学技术解析HCBD降解功能菌群结构和潜在互作机制、HCBD厌氧降解微生物的分离与纯化,以及HCBD厌氧降解菌剂的开发与污染场地原位生物修复应用等。     

Biodegradation of soluble aromatic compounds of jet fuel under anaerobic conditions: laboratory batch experiments

Laboratory batch experiments were performed with contaminated aquifer sediments and four soluble aromatic components of jet fuel to assess their biodegradation under anaerobic conditions. The biodegradation of four aromatic compounds, toluene, o-xylene, 1,2,4-trimethylbenzene (TMB), and naphthalene, separately or together, was investigated under strictly anaerobic conditions in the dark for a period of 160 days. Of the aromatic compounds, toluene and o-xylene were degraded both as a single substrate and in a mixture with the other aromatic compounds, while TMB was not biodegraded as a single substrate, but was biodegraded in the presence of the other aromatic hydrocarbons. Substrate interaction is thus significant in the biodegradation of TMB. Biodegradation of naphthalene was not observed, either as a single substrate or in a mixture of other aromatic hydrocarbons. Although redox conditions were dominated by iron reduction, a clear relation between degradation and sulfate reduction was observed. Methanogenesis took place during the later stages of incubation. However, the large background of Fe(II) masked the increase of Fe(II) concentration due to iron reduction. Thus, although microbial reduction of Fe(III) is an important process, the evidence is not conclusive. Our results have shown that a better understanding of the degradation of complex mixtures of hydrocarbons under anaerobic conditions is important in the application of natural attenuation as a remedial method for soil and groundwater contamination.     

Multisubstrate biodegradation kinetics of naphthalene, phenanthrene, and pyrene mixtures.

Biodegradation kinetics of naphthalene, phenanthrene and pyrene were studied in sole-substrate systems, and in binary and ternary mixtures to examine substrate interactions. The experiments were conducted in aerobic batch aqueous systems inoculated with a mixed culture that had been isolated from soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Monod kinetic parameters and yield coefficients for the individual compounds were estimated from substrate depletion and CO(2) evolution rate data in sole-substrate experiments. In all three binary mixture experiments, biodegradation kinetics were comparable to the sole-substrate kinetics. In the ternary mixture, biodegradation of naphthalene was inhibited and the biodegradation rates of phenanthrene and pyrene were enhanced. A multisubstrate form of the Monod kinetic model was found to adequately predict substrate interactions in the binary and ternary mixtures using only the parameters derived from sole-substrate experiments. Numerical simulations of biomass growth kinetics explain the observed range of behaviors in PAH mixtures. In general, the biodegradation rates of the more degradable and abundant compounds are reduced due to competitive inhibition, but enhanced biodegradation of the more recalcitrant PAHs occurs due to simultaneous biomass growth on multiple substrates. In PAH-contaminated environments, substrate interactions may be very large due to additive effects from the large number of compounds present.     

Identification and degradation characterization of hexachlorobutadiene degrading strain Serratia marcescens HL1

A bacterium (strain HL1) capable of growing with hexachlorobutadiene (HCBD) as sole carbon and energy sources was isolated from a mixture of soil contaminated with HCBD and activated sludge obtained from petrochemical plant wastewater treatment plant by using enrichment culture. Biochemical characteristics and phylogenetic analysis based on 16S rDNA sequence indicate that strain HL1 clearly belongs to Serratia marcescens sp. Resting cells of strain HL1 were found to remove HCBD from culture fluids with the concomitant release of chloride ion under aerobic conditions. The ranges of pH value and temperature for satisfactory growth of strain HL1 cells were from 7.0 to 8.0 and 25 to 30 degrees C, respectively. Capability of resting cells to degrade HCBD was induced by HCBD in the culture fluids. HCBD (20mg/l) was removed from culture fluids by resting cells in 4 d without lag phase, but for 50mg/l and 80mg/l HCBD 7 days were needed with lag phase. Growth of strain HL1 cells was inhibited by HCBD at the concentration up to 160mg/l. First order kinetics could be fitted to the biodegradation of HCBD by HL1 cells after lag phase at initial concentrations of 20, 50, and 80mg/l. Strain HL1 also showed strong capacity to degrade chloroprene, trichloroethylene, tetrachloroethylene, and vinyl chloride at solely initial concentration of 50mg/l. Results could offer useful information for the application of strain HL1 in bioremediation or control of HCBD-polluted environment.     

Biodegradation of diesel/biodiesel blends by a consortium of hydrocarbon degraders: effect of the type of blend and the addition of biosurfactants

Biodegradation experiments for diesel/biodiesel blends in liquid cultures by-petroleum degrading microbial consortium showed that for low amendments of biodiesel (10%) the overall biodegradation efficiency of the mixture after seven days was lower than for petroleum diesel fuel. Preferential usage of methyl esters in the broad biodiesel concentration range and diminished biodegradation of petroleum hydrocarbons for 10% biodiesel blend was confirmed. Rhamnolipids improved biodegradation efficiency only for blends with low content of biodiesel. Emulsion formation experiments showed that biodiesel amendments significantly affected dispersion of fuel mixtures in water. The presence of rhamnolipids biosurfactant affected stability of such emulsions and altered cell surface properties of tested consortium.     

专一营养与兼性甲烷氧化菌降解氯代烃的研究现状、动力学分析及展望

生物修复技术被认为是氯代烃类污染物处理处置的最有效途径之一,而甲烷氧化菌在该领域表现出较大的应用潜力。近期研究发现,突破了仅能利用单碳化合物的局限,兼性甲烷氧化菌能够利用多种底物降解氯代烃,这一独特的新陈代谢特性,使其在污染物生物处置领域逐渐受到关注。结合本课题组研究成果,对甲烷氧化菌降解氯代烃进行了全面总结,主要包括:分析了不同菌株(纯菌株和混合菌株)对不同氯代烃的降解效果;比较了不同类型甲烷单加氧酶在不同底物体系中的活性表达和催化特性;总结了模型菌株甲基弯菌Methylosinus trichosporium OB3b降解氯代烃的动力学特性;概述了兼性甲烷氧化菌株降解氯代烃的特性及其应用潜力;最后讨论了甲烷氧化菌降解氯代烃存在的问题及未来发展方向。     

Biodegradation of individual and multiple chlorinated aliphatic hydrocarbons by methane-oxidizing cultures.

The microbial degradation of chlorinated and nonchlorinated methanes, ethanes, and ethanes by a mixed methane-oxidizing culture grown under chemostat and batch conditions is evaluated and compared with that by two pure methanotrophic strains: CAC1 (isolated from the mixed culture) and Methylosinus trichosporium OB3b. With the exception of 1,1-dichloroethylene, the transformation capacity (Tc) for each chlorinated aliphatic hydrocarbon was generally found to be in inverse proportion to its chlorine content within each aliphatic group (i.e., methanes, ethanes, and ethenes), whereas similar trends were not observed for degradation rate constants. Tc trends were similar for all methane-oxidizing cultures tested. None of the cultures were able to degrade the fully chlorinated aliphatics such as perchloroethylene and carbon tetrachloride. Of the four cultures tested, the chemostat-grown mixed culture exhibited the highest Tc for trichloroethylene, cis-1,2-dichloroethylene, tetrachloroethane, 1,1,1-trichloroethane, and 1,2-dichloroethane, whereas the pure batch-grown OB3b culture exhibited the highest Tc for all other compounds tested. The product toxicity of chlorinated aliphatic hydrocarbons in a mixture containing multiple compounds was cumulative and predictable when using parameters measured from the degradation of individual compounds. The Tc for each chlorinated aliphatic hydrocarbon in a mixture (Tcmix) and the total Tc for the mixture (sigma Tcmix) are functions of the individual Tc, the initial substrate concentration (S0), and the first-order rate constant (k/Ks) of each compound in the mixture, indicating the importance of identifying the properties and compositions of all potentially degradable compounds in a contaminant mixture.     

Riboflavin- and cobalamin-mediated biodegradation of chloroform in a methanogenic consortium

Chloroform (CF) is an important priority pollutant contaminating groundwater. Reductive dechlorination by anaerobic microorganisms is a promising strategy towards the remediation of CF. The objective of this study was to evaluate the use of redox active vitamins as electron shuttles to enhance the anaerobic biodegradation of CF in an unadapted methanogenic consortium not previously exposed to chlorinated compounds. Only negligible degradation of CF was observed in control cultures lacking redox active vitamins. The addition of riboflavin (RF), cyanocobalamin (CNB12), and hydroxycobalamin (HOB12) enabled biodegradation of CF. The reactions were predominantly catalyzed biologically as evidenced by the lack of any CF conversion in heat-killed controls amended with the cobalamins or minor conversion with RF. In live cultures, significant increases in the rate of CF conversion was observed at substoichiometric molar ratios as low as 0.1 to 0.01 vitamin:CF for RF and CNB12, respectively. At the highest molar vitamin:CF ratios tested of 0.2, the first-order rate constant of CF degradation was 5.3- and 91-fold higher in RF and CNB12 amended cultures, respectively, compared to the unamended control culture. The distribution of biotransformation products was highly impacted by the type of redox active vitamin utilized. Cultures supplemented with RF provided high yields of dichloromethane (DCM). On the other hand, cobalamins promoted the near complete mineralization of organochlorine in CF to inorganic chloride and lowered the yield of DCM. In cultures where no or little CF bioconversion occurred, prolonged exposure to CF resulted in cell lysis, as evidenced by the release of intracellular chloride. The results taken as a whole suggest that the anaerobic bioremediation of CF-contaminated sites can greatly be improved with strategies aimed at increasing the concentration of redox active vitamins.     

Biodegradation kinetics of select polycyclic aromatic hydrocarbon (PAH) mixtures by <Emphasis Type="Italic">Sphingomonas paucimobilis</Emphasis> EPA505

Many contaminated sites commonly have complex mixtures of polycyclic aromatic hydrocarbons (PAHs) whose individual microbial biodegradation may be altered in mixtures. Biodegradation kinetics for fluorene, naphthalene, 1,5-dimethylnaphthalene and 1-methylfluorene were evaluated in sole substrate, binary and ternary systems using Sphingomonas paucimobilis EPA505. The first order rate constants for fluorene, naphthalene, 1,5-dimethylnaphthalene, and 1-methylfluorene were comparable; yet Monod parameters were significantly different for the tested PAHs. S. paucimobilis completely degraded all the components in binary and ternary mixtures; however, the initial degradation rates of individual components decreased in the presence of competitive PAHs. Results from the mixture experiments indicate competitive interactions, demonstrated mathematically. The generated model appropriately predicted the biodegradation kinetics in mixtures using parameter estimates from the sole substrate experiments, validating the hypothesis of a common rate-determining step. Biodegradation kinetics in mixtures were affected by the affinity coefficients of the co-occurring PAHs and mixture composition. Experiments with equal concentrations of substrates demonstrated the effect of concentration on competitive inhibition. Ternary experiments with naphthalene, 1,5-dimethylnaphthalene and 1-methylfluorene revealed delayed degradation, where depletion of naphthalene and 1,5-dimethylnapthalene occurred rapidly only after the complete removal of 1-methylfluorene. The substrate interactions observed in mixtures require a multisubstrate model to account for simultaneous degradation of substrates. PAH contaminated sites are far more complex than even ternary mixtures; however these studies clearly demonstrate the effect that interactions can have on individual chemical kinetics. Consequently, predicting natural or enhanced degradation of PAHs cannot be based on single compound kinetics as this assumption would likely overestimate the rate of disappearance.     

Biodegradation and bioremediation of hydrocarbons in extreme environments

Many hydrocarbon-contaminated environments are characterized by low or elevated temperatures, acidic or alkaline pH, high salt concentrations, or high pressure, Hydrocarbon-degrading microorganisms, adapted to grow and thrive in these environments, play an important role in the biological treatment of polluted extreme habitats. The biodegradation (transformation or mineralization) of a wide range of hydrocarbons, including aliphatic, aromatic, halogenated and nitrated compounds, has been shown to occur in various extreme habitats. The biodegradation of many components of petroleum hydrocarbons has been reported in a variety of terrestrial and marine cold ecosystems. Cold-adapted hydrocarbon degraders are also useful for wastewater treatment. The use of thermophiles for biodegradation of hydrocarbons with low water solubility is of interest, as solubility and thus bioavailability, are enhanced at elevated temperatures. Thermophiles, predominantly bacilli, possess a substantial potential for the degradation of environmental pollutants, including all major classes. Indigenous thermophilic hydrocarbon degraders are of special significance for the bioremediation of oil-polluted desert soil. Some studies have investigated composting as a bioremediation process. Hydrocarbon biodegradation in the presence of high salt concentrations is of interest for the bioremediation of oil-polluted salt marshes and industrial wastewaters, contaminated with aromatic hydrocarbons or with chlorinated hydrocarbons. Our knowledge of the biodegradation potential of acidophilic, alkaliphilic, or barophilic microorganisms is limited.     

Biodegradation of xenobiotics by anaerobic bacteria

Xenobiotic biodegradation under anaerobic conditions such as in groundwater, sediment, landfill, sludge digesters and bioreactors has gained increasing attention over the last two decades. This review gives a broad overview of our current understanding of and recent advances in anaerobic biodegradation of five selected groups of xenobiotic compounds (petroleum hydrocarbons and fuel additives, nitroaromatic compounds and explosives, chlorinated aliphatic and aromatic compounds, pesticides, and surfactants). Significant advances have been made toward the isolation of bacterial cultures, elucidation of biochemical mechanisms, and laboratory and field scale applications for xenobiotic removal. For certain highly chlorinated hydrocarbons (e.g., tetrachlorethylene), anaerobic processes cannot be easily substituted with current aerobic processes. For petroleum hydrocarbons, although aerobic processes are generally used, anaerobic biodegradation is significant under certain circumstances (e.g., O₂-depleted aquifers, oil spilled in marshes). For persistent compounds including polychlorinated biphenyls, dioxins, and DDT, anaerobic processes are slow for remedial application, but can be a significant long-term avenue for natural attenuation. In some cases, a sequential anaerobic-aerobic strategy is needed for total destruction of xenobiotic compounds. Several points for future research are also presented in this review.     

Biodegradation of selected UV-irradiated and non-irradiated polycyclic aromatic hydrocarbons (PAHs)

Biodegradation of UV-irradiated anthracene, pyrene,benz[a]anthracene,and dibenz[a,h]anthracene was comparedto that of the non-irradiated samples, individuallyand in synthetic mixtures with enrichment cultures.Combined treatment was repeated for individual anthraceneand for the PAH mixture with Sphingomonas sp.strain EPA 505 and Sphingomonas yanoikuyae.Enrichment culture studies were performed on the PAHmixtures in the presence of the main photoproduct ofanthracene, pure 9,10-anthracenedione. Photochemicallypretreated creosote solutions were also subjected tobiodegradation and the results were compared tothose of the non-irradiated solutions. The primaryinterest was on 16 polycyclic aromatic hydrocarbons(PAHs) listed as priority pollutants by European Union(EU) and the United States Environmental ProtectionAgency (USEPA). Irradiation accelerated thebiodegradation onset for anthracene, pyrene, andbenz[a]anthracene when they were treatedindividually. The biodegradation of irradiatedpyrene started with no lag phase andwas complete by 122 h whereas biodegradation of thenon-irradiated sample had a lag of 280 h andresulted in complete degradation by 720 h. Biodegradation ofPAHs was accelerated in synthetic mixtures, especiallyin the presence of pure 9,10-anthracenedione.In general, irradiation had no effect on the biodegradation of PAHsincubated in synthetic mixtures or with pure cultures. Undercurrent experimental conditions, the UV-irradiation invariablyreduced the biodegradation of PAHs in creosote. Based onthe results of the present and previous photochemical-biologicalstudies of PAHs, the influence of the photochemical pretreatmenton the biodegradation is highly dependent on the compoundsbeing treated and other process parameters.     

Biodegradation Rates for Fuel Hydrocarbons and Chlorinated Solvents in Groundwater

Numerous studies presented in the general literature have shown that the key mechanism affecting the rate and extent of migration of a contaminant plume is biodegradation since it removes contaminant mass and reduces average plume concentrations. This paper attempts to address the importance of biodegradation for fuel and chlorinated solvent plumes and to present a comprehensive review of rates of biodegradation obtained from field and laboratory studies. Data from approximately 280 studies are statistically analyzed to determine ranges of biodegradation rates for various contaminants under different redox conditions. A review of 133 studies for fuel hydrocarbons has yielded first-order biodegradation coefficients up to 0.445 day^-1 under aerobic conditions and up to 0.522^-1 under anaerobic conditions in 90% of the cases. A median rate constant for benzene of 0.3% day^-1 was estimated from all studies, while those for toluene, ethylbenzene, and xylenes were estimated to be 4, 0.3, and 0.4% day^-1, respectively. On the other hand, data from 138 studies with chlorinated solvents show that the less chlorinated compounds biodegrade in the 90% of the cases with rate constants lower than 1.35 day^-1 under aerobic conditions and that highly chlorinated compounds biodegrade with decay coefficients up to 1.28 day^-1 in 90% of the anoxic experiments. Median decay coefficients derived from all studies were 4.9, 0.07, 0.42, 0.86, 1.02, 0.44, and 4.7 day^-1 for carbon tetrachloride, dichloroethane (DCA), cis-1,2-dichloroethene (cis-1,2-DCE), tetrachloroethene (PCE), trichloroethane (TCA), trichloroethene (TCE), and vinyl chloride, respectively. The rate constants presented in this study can be used in screening and modeling studies and to guide the assessment of natural attenuation as a viable remedial technology at contaminated sites. represent a compilation of available literature data.     

Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds

The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d^-1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions.     

Long-Term Sustainability of Reductive Dechlorination Reactions at Chlorinatedsolvents Sites

The sustainability of biodegradation reactions is of interest at Type 1 chlorinated solvent sites where monitored natural attenuation is being considered as a remedial alternative. Type 1 chlorinated solvent sites are sites undergoing reductive dechlorination where anthropogenic substrates (such as landfill leachate or fermentable organics in the waste materials) ferment to produce hydrogen, a key electron donor. A framework is provided that classifies Type 1 chlorinated solvent sites based on the relative amounts and the depletion rates of the electron donors and the electron acceptors (i.e., chlorinated solvents). Expressions are presented for estimating the total electron donor demand due to the presence of solvents and competing electron acceptors such as dissolved oxygen, nitrate, and sulfate. Finally, a database of 13 chlorinated solvent sites was analyzed to estimate the median and maximum mass discharge rate for dissolved oxygen, nitrate, and sulfate flowing into chlorinated solvent plumes. These values were then used to calculate the amount of hydrogen equivalents and potential for lost perchloroethylene (PCE) biodegradation represented by the inflow of these competing electron acceptors. The median and maximum mass of PCE biodegradation lost due to competing electron acceptors, assuming 100% efficiency, was 226 and 4621 kg year(-1), respectively.     

Changes in iso- and n-alkane distribution during biodegradation of crude oil under nitrate and sulphate reducing conditions

Crude oil consists of a large number of hydrocarbons with different susceptibility to microbial degradation. The influence of hydrocarbon structure and molecular weight on hydrocarbon biodegradation under anaerobic conditions is not fully explored. In this study oxygen, nitrate and sulphate served as terminal electron acceptors (TEAs) for the microbial degradation of a paraffin-rich crude oil in a freshly contaminated soil. During 185 days of incubation, alkanes from n-C11 to n-C39, three n- to iso-alkane ratios commonly used as weathering indicators and the unresolved complex mixture (UCM) were quantified and statistically analyzed. The use of different TEAs for hydrocarbon degradation resulted in dissimilar degradative patterns for n- and iso-alkanes. While n-alkane biodegradation followed well-established patterns under aerobic conditions, lower molecular weight alkanes were found to be more recalcitrant than mid- to high-molecular weight alkanes under nitrate-reducing conditions. Biodegradation with sulphate as the TEA was most pronounced for long-chain (n-C32 to n-C39) alkanes. The observation of increasing ratios of n-C17 to pristane and of n-C18 to phytane provides first evidence of the preferential degradation of branched over normal alkanes under sulphate reducing conditions. The formation of distinctly different n- and iso-alkane biodegradation fingerprints under different electron accepting conditions may be used to assess the occurrence of specific degradation processes at a contaminated site. The use of n- to iso-alkane ratios for this purpose may require adjustment if applied for anaerobic sites.     

Pollutant degradation by a Methylocystis strain SB2 grown on ethanol: bioremediation via facultative methanotrophy

A facultative methanotroph, Methylocystis strain SB2, was examined for its ability to degrade chlorinated hydrocarbons when grown on methane or ethanol. Strain SB2 grown on methane degraded vinyl chloride (VC), trans-dichloroethylene (t-DCE), trichloroethylene (TCE), 1,1,1-trichloroethane (1,1,1-TCA), and chloroform (CF), but not dichloromethane (DCM). Growth on methane was reduced in the presence of any chlorinated hydrocarbon. Strain SB2 grown on ethanol degraded VC, t-DCE, and TCE, and 1,1,1-TCA, but not DCM or CF. With the exception of 1,1,1-TCA, the growth of strain SB2 on ethanol was not affected by any individual chlorinated hydrocarbon. No degradation of any chlorinated hydrocarbon was observed when acetylene was added to ethanol-grown cultures, indicating that this degradation was due to particulate methane monooxygenase (pMMO) activity. When mixtures of chlorinated alkanes or alkenes were added to cultures growing on methane or ethanol, chlorinated alkene degradation occurred, but chlorinated alkanes were not, and growth was reduced on both methane and ethanol. Collectively, these data indicate that competitive inhibition of pMMO activity limits methanotrophic growth and pollutant degradation. Facultative methanotrophy may thus be useful to extend the utility of methanotrophs for bioremediation as the use of alternative growth substrates allows for pMMO activity to be focused on pollutant degradation.     

Modeling Chlorinated Solvent Bioremediation Using Hydrogen Release Compound (HRC)

Chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. One approach that has been used to manage these contaminants is in situ bioremediation, where an electron donor is added to contaminated groundwater to stimulate indigenous bacteria to degrade the chlorinated compounds. A technique that is increasingly being used to supply electron donor to the subsurface involves application of a commercial product with the trade name Hydrogen Release Compound (HRC). HRC is a viscous fluid that releases lactic acid, which subsequently is metabolized to provide molecular hydrogen as an electron donor. This study investigates application of HRC to remediate a site contaminated with TCE. A user-defined dual-Monod biodegradation reaction module was developed for the RT3D-reactive transport code to simulate in situ biodegradation of TCE by reductive dehalogenation stimulated by release of molecular hydrogen in the subsurface as a result of HRC injection. The model was used to show how a remediation system using HRC to stimulate reductive dehalogenation could be designed, and how mixing, as quantified by hydraulic conductivity and dispersivity, impacts the system design.     

Characterisation of biodegradation capacities of environmental microflorae for diesel oil by comprehensive two-dimensional gas chromatography

In contaminated soils, efficiency of natural attenuation or engineered bioremediation largely depends on biodegradation capacities of the local microflorae. In the present study, the biodegradation capacities of various microflorae towards diesel oil were determined in laboratory conditions. Microflorae were collected from 9 contaminated and 10 uncontaminated soil samples and were compared to urban wastewater activated sludge. The recalcitrance of hydrocarbons in tests was characterised using both gas chromatography (GC) and comprehensive two-dimensional gas chromatography (GC×GC). The microflorae from contaminated soils were found to exhibit higher degradation capacities than those from uncontaminated soil and activated sludge. In cultures inoculated by contaminated-soil microflorae, 80% of diesel oil on an average was consumed over 4-week incubation compared to only 64% in uncontaminated soil and 60% in activated sludge cultures. As shown by GC, n-alkanes of diesel oil were totally utilised by each microflora but differentiated degradation extents were observed for cyclic and branched hydrocarbons. The enhanced degradation capacities of impacted-soil microflorae resulted probably from an adaptation to the hydrocarbon contaminants but a similar adaptation was noted in uncontaminated soils when conifer trees might have released natural hydrocarbons. GC×GC showed that a contaminated-soil microflora removed all aromatics and all branched alkanes containing less than C₁₅. The most recalcitrant compounds were the branched and cyclic alkanes with 15–23 atoms of carbon.     

Design of bacterial defined mixed cultures for biodegradation of specific crude oil fractions, using population dynamics analysis by DGGE

Hydrocarbon-degrading bacteria isolated from oil-polluted soils, were used to design three defined mixed cultures (DMC) for biodegradation of Maya crude oil fractions. The first degrading culture, DMC A was made up with 10 strains. Design of DMC B (six strains) and DMC C (three strains) was based on DGGE profiles obtained throughout biodegradation assays of different petroleum fractions. Biodegradation of the aliphatic fraction (10 000 mg l⁻¹) and an aromatic–polar mixture (5000 mg l⁻¹) was evaluated for the DMC B. Biodegradation of total hydrocarbons (10 000 mg l⁻¹) and its fractions was evaluated for DMC B and DMC C. During biodegradation assays, O₂ consumption and CO₂ production were assessed by respirometry, while population dynamics of predominant strains was based on PCR-DGGE profiles of partial 16S rDNA. Aliphatic fraction was completely biodegraded by DMC B, while degradation of the aromatic–polar mixture was 12.5% and for total hydrocarbons 40.5%. DMC B was able to degrade the aromatic fraction (31%) and even the polar fraction (19.6%) present in total hydrocarbons. DMC C degraded the aromatic and polar fractions (5.6% and 2%, respectively) present in total hydrocarbons. DGGE profiles of the DMCs indicated that Pseudomonas sp., Gordonia rubripertincta and a non-identified strain were predominant and probably responsible of the hydrocarbons biodegradation. The use of DGGE-fingerprinting to track microbial populations, allowed selecting strains to design efficient oil-degrading defined mixed cultures.