Microbial oxidation of gaseous hydrocarbons: epoxidation of C2 to C4 n-alkenes by methylotrophic bacteria.

Over 20 new cultures of methane-utilizing microbes, including obligate (types I and III) and facultative methylotrophic bacteria were isolated. In addition to their ability to oxidize methane to methanol, resting cell-suspensions of three distinct types of methane-grown bacteria (Methylosinus trichosporium OB3b [type II, obligate]; Methylococcus capsulatus CRL M1 NRRL B-11219 [type I, obligate]; and Methylobacterium organophilum CRL-26 NRRL B-11222 [facultative]) oxidize C2 to C4 n-alkenes to their corresponding 1,2-epoxides. The product 1,2-epoxides are not further metabolized and accumulate extracellularly. Methanol-grown cells do not have either the epoxidation or the hydroxylation activities. Among the substrate gaseous alkenes, propylene is oxidized at the highest rate. Methane inhibits the epoxidation of propylene. The stoichiometry of the consumption of propylene and oxygen and the production of propylene oxide is 1:1:1. The optimal conditions for in vivo epoxidation are described. Results from inhibition studies indicate that the same monooxygenase system catalyzes both the hydroxylation and the epoxidation reactions. Both the hydroxylation and epoxidation activities are located in the cell-free particulate fraction precipitated between 10,000 and 40,000 x g centrifugation.     

Epoxidation of Short-Chain Alkenes by Resting-Cell Suspensions of Propane-Grown Bacteria

Sixteen new cultures of propane-utilizing bacteria were isolated from lake water from Warinanco Park, Linden, N.J. and from lake and soil samples from Bayway Refinery, Linden, N.J. In addition, 19 known cultures obtained from culture collections were also found to be able to grow on propane as the sole carbon and energy source. In addition to their ability to oxidize n-alkanes, resting-cell suspensions of both new cultures and known cultures grown on propane oxidize short-chain alkenes to their corresponding 1,2-epoxides. Among the substrate alkenes, propylene was oxidized at the highest rate. In contrast to the case with methylotrophic bacteria, the product epoxides are further metabolized. Propane and other gaseous n-alkanes inhibit the epoxidation of propylene. The optimum conditions for in vivo epoxidation are described. Results from inhibition studies indicate that a propane monooxygenase system catalyzes both the epoxidation and hydroxylation reactions. Experiments with cell-free extracts show that both hydroxylation and epoxidation activities are located in the soluble fraction obtained after 80,000 × g centrifugation.     

Conversion of Unsaturated Fatty Acids by Bacteria Isolated from Compost

A compost mixture amended with soybean oil was enriched in microorganisms that transformed unsaturated fatty acids (UFAs). When oleic acid or 10-ketostearic acid was the selective fatty acid, Sphingobacterium thalpophilum (NRRL B-23206, NRRL B-23208, NRRL B-23209, NRRL B-23210, NRRL B-23211, NRRL B-23212), Acinetobacter spp. (NRRL B-23207, NRRL B-23213), and Enterobacter cloacae (NRRL B-23264, NRRL B-23265, NRRL B-23266) represented isolates that produced either hydroxystearic acid, ketostearic acid, or incomplete decarboxylations. When ricinoleic (12-hydroxy-9-octadecenoic) acid was the selective UFA, Enterobacter cloacae (NRRL B-23257, NRRL B-23267) and Escherichia sp. (NRRL B-23259) produced 12-C and 14-C homologous compounds, and Pseudomonas aeruginosa (NRRL B-23256, NRRL B-23260) converted ricinoleate to a trihydroxyoctadecenoate product. Also, various Enterobacter, Pseudomonas, and Serratia spp. appeared to decarboxylate linoleate substrate incompletely. These saprophytic, compost bacteria were aerobic or facultative anaerobic Gram-negative and decomposed UFAs through decarboxylation, hydroxylation, and hydroperoxidation mechanisms. Received: 3 November 1998 / Accepted: 30 November 1998     

Microbial oxidation of gaseous hydrocarbons: production of methyl ketones from their corresponding secondary alcohols by methane- and methanol-grown microbes.

Cultures of methane- or methanol-utilizing microbes, including obligate (both types I and II) and facultative methylotrophic bacteria, obligate methanol utilizers, and methanol-grown yeasts were isolated from lake water of Warinanco Park, Linden, N.J., and lake and soil samples of Bayway Refinery, Linden, N.J. Resting-cell suspensions of these, and of other known C1-utilizing microbes, oxidized secondary alcohols to their corresponding methyl ketones. The product methyl ketones accumulated extracellularly. Succinate-grown cells of facultative methylotrophs did not oxidize secondary alcohols. Among the secondary alcohols, 2-butanol was oxidized at the highest rate. The optimal conditions for in vivo methyl ketone formation were compared among five different types of C1-utilizing microbes. Some enzymatic degradation of 2-butanone was observed. The product, 2-butanone, did not inhibit the oxidation of 2-butanol. The rate of the 2-butanone production was linear for the first 4 h of incubation for all five cultures tested. A yeast culture had the highest production rate. The optimum temperature for the production of 2-butanone was 35 degrees C for all the bacteria tested. The yeast culture had a higher temperature optimum (40 degrees C), and there was a reasonably high 2-butanone production rate even at 45 degrees C. Metal-chelating agents inhibit the production of 2-butanone, suggesting the involvement of metal(s) in the oxidation of secondary alcohols. Secondary alcohol dehydrogenase activity was found in the cell-free soluble extract of sonically disrupted cells. The cell-free system requires a cofactor, specifically nicotinamide adenine dinucleotide, for its activity. This is the first report of a nicotinamide adenine dinucleotide-dependent, secondary alcohol-specific enzyme.     

Trimethylamine metabolism in obligate and facultative methylotrophs

1. Twelve bacterial isolates that grow with trimethylamine as sole source of carbon and energy were obtained in pure culture. All the isolates grow on methylamine, dimethylamine and trimethylamine. One isolate, bacterium 4B6, grows only on these methylamines whereas another isolate, bacterium C2A1, also grows on methanol but neither grows on methane; these two organisms are obligate methylotrophs. The other ten isolates grow on a variety of C(i) and other organic compounds and are therefore facultative methylotrophs. 2. Washed suspensions of the obligate methylotrophs bacteria 4B6 and C2A1, and of the facultative methylotrophs bacterium 5B1 and Pseudomonas 3A2, all grown on trimethylamine, oxidize trimethylamine, dimethylamine, formaldehyde and formate; only bacterium 5B1 and Ps. 3A2 oxidize trimethylamine N-oxide; only bacterium 4B6 does not oxidize methylamine. 3. Cell-free extracts of trimethylamine-grown bacteria 4B6 and C2A1 contain a trimethylamine dehydrogenase that requires phenazine methosulphate as primary hydrogen acceptor, and evidence is presented that this enzyme is important for the growth of bacterium 4B6 on trimethylamine. 4. Cell-free extracts of eight facultative methylotrophs, including bacterium 5B1 and Ps. 3A2, do not contain trimethylamine dehydrogenase but contain instead a trimethylamine monooxygenase and trimethylamine N-oxide demethylase. It is concluded that two different pathways for the oxidation of trimethylamine occur amongst the isolates.     

Purification and properties of a NAD-linked 1,2-propanediol dehydrogenase from propane-grown Pseudomonas fluorescens NRRL B-1244

NAD-dependent 1,2-propanediol dehydrogenase (EC 1.1.1.4) activity was detected in cell-free crude extracts of various propane-grown bacteria. The enzyme activity was much lower in 1-propanol-grown cells than in propane-grown cells of Pseudomonas fluorescens NRRL B-1244, indicating that the enzyme may be inducible by metabolites of propane subterminal oxidation. 1,2-Propanediol dehydrogenase was purified from propane-grown Ps. fluorescens NRRL B-1244. The purified enzyme fraction shows a single-protein band upon acrylamide gel electrophoresis and has a molecular weight of 760,000. It consists of 10 subunits of identical molecular weight (77,600). It oxidizes diols that possess either two adjacent hydroxy groups, or a hydroxy group with an adjacent carbonyl group. Primary and secondary alcohols are not oxidized. The pH and temperature optima for 1,2-propanediol dehydrogenase are 8.5 and 20-25 degrees C, respectively. The activation energy calculated is 5.76 kcal/mol. 1,2-Propanediol dehydrogenase does not catalyze the reduction of acetol or acetoin in the presence of NADH (reverse reaction). The Km values at 25 degrees C, pH 7.0, buffer solution for 1,2-propan1,2-propanediol dehydrogenase are 8.5 and 20-25 degrees C, respectively. The activation energy calculated is 5.76 kcal/mol. 1,2-Propanediol dehydrogenase does not catalyze the reduction of acetol or acetoin in the presence of NADH (reverse reaction). The Km values at 25 degrees C, pH 7.0, buffer solution for 1,2-propan1,2-propanediol dehydrogenase are 8.5 and 20-25 degrees C, respectively. The activation energy calculated is 5.76 kcal/mol. 1,2-Propanediol dehydrogenase does not catalyze the reduction of acetol or acetoin in the presence of NADH (reverse reaction). The Km values at 25 degrees C, pH 7.0, buffer solution for 1,2-propanediol and NAD are 2 X 10(-2) and 9 X 10(-5) M, respectively. The 1,2-propanediol dehydrogenase activity was inhibited by strong thiol reagents, but not by metal-chelating agents. The amino acid composition of the purified enzyme was determined. Antisera prepared against purified 1,2-propanediol dehydrogenase from propane-grown Ps. fluorescens NRRL B-1244 formed homologous precipitin bands with isofunctional enzymes derived from propane-grown Arthrobacter sp. NRRL B-11315, Nocardia paraffinica ATCC 21198, and Mycobacterium sp. P2y, but not from propane-grown Pseudomonas multivorans ATCC 17616 and Brevibacterium sp. ATCC 14649, or 1-propanol-grown Ps. fluorescens NRRL B-1244. Isofunctional enzymes derived from methane-grown methylotrophs also showed different immunological and catalytic properties.     

Microbial Oxidation of Gaseous Hydrocarbons: Production of Methyl Ketones from Their Corresponding Secondary Alcohols by Methane- and Methanol-Grown Microbes

Cultures of methane- or methanol-utilizing microbes, including obligate (both types I and II) and facultative methylotrophic bacteria, obligate methanol utilizers, and methanol-grown yeasts were isolated from lake water of Warinanco Park, Linden, N.J., and lake and soil samples of Bayway Refinery, Linden, N.J. Resting-cell suspensions of these, and of other known C1-utilizing microbes, oxidized secondary alcohols to their corresponding methyl ketones. The product methyl ketones accumulated extracellularly. Succinate-grown cells of facultative methylotrophs did not oxidize secondary alcohols. Among the secondary alcohols, 2-butanol was oxidized at the highest rate. The optimal conditions for in vivo methyl ketone formation were compared among five different types of C1-utilizing microbes. Some enzymatic degradation of 2-butanone was observed. The product, 2-butanone, did not inhibit the oxidation of 2-butanol. The rate of the 2-butanone production was linear for the first 4 h of incubation for all five cultures tested. A yeast culture had the highest production rate. The optimum temperature for the production of 2-butanone was 35°C for all the bacteria tested. The yeast culture had a higher temperature optimum (40°C), and there was a reasonably high 2-butanone production rate even at 45°C. Metal-chelating agents inhibit the production of 2-butanone, suggesting the involvement of metal(s) in the oxidation of secondary alcohols. Secondary alcohol dehydrogenase activity was found in the cell-free soluble extract of sonically disrupted cells. The cell-free system requires a cofactor, specifically nicotinamide adenine dinucleotide, for its activity. This is the first report of a nicotinamide adenine dinucleotide-dependent, secondary alcohol-specific enzyme.     

Synthesis and biological activities of new hydrazide derivatives

The synthesis of a new series of imidazo[1,2-a]pyrazine-2-carboxylic acid arylidene-hydrazides is described. The chemical structures of the compounds were elucidated by IR, (1)H-NMR, FAB(+)-MS spectral data. Their biological activity against various bacteria, fungi species, and Mycobacterium tuberculosis was investigated. Antibacterial activity was measured against Escherichia coli (NRRL B-3704), Staphylococcus aureus (NRRL B-767), Salmonella typhimurium (NRRL B-4420), Proteus vulgaris (NRLL B-123), Enterococcus faecalis (isolated obtained from Faculty of Medicine Osmangazi University, Eskisehir, Turkey), Pseudomonas aeruginosa (NRRL B-23 27853), Klebsiella spp. (isolated obtained from Faculty of Medicine Osmangazi University, Eskisehir, Turkey), while antifungal activity was evaluated against Candida albicans (isolates obtained from Osmangazi Uni. Fac.of Medicine), Candida glabrata (isolates obtained from Osmangazi Uni. Fac.of Medicine). Compounds were also evaluated for antituberculosis activity against Mycobacterium tuberculosis H(37)Rv using the BACTEC 460 radiometric system and BACTEC 12B medium. The compounds showed moderate inhibitor effects against human pathogenic microorganisms., whereas the preliminary results indicated that all of the tested compounds were inactive against Mycobacterium tuberculosis H(37)Rv.     

Description of the erythromycin-producing bacterium Arthrobacter sp. strain NRRL B-3381 as Aeromicrobium erythreum gen. nov., sp. nov

Arthrobacter sp. strain NRRL B-3381T (T = type strain) is a nonmycelial, nonsporulating actinomycete that produces the macrolide antibiotic erythromycin. This bacterium differs in many ways from the type species of the genus Arthrobacter (Arthrobacter globiformis), suggesting that a taxonomic revision is appropriate. The G + C content of strain NRRL B-3381T DNA is 71 to 73 mol%, and the peptidoglycan of this organism contains LL-diaminopimelic acid. Evolutionary distance data obtained from 16S rRNA sequences identified NRRL B-3381T as the deepest branching member of the Nocardioides group of actinomycetes. The principal long-chain fatty acids which we identified that distinguished strain NRRL B-3381T from related G + C-rich bacteria were 10-methyloctadecanoic (tuberculosteric), octadecenoic, and hexadecanoic acids. These characteristics, together with phage typing and biochemical characteristics, form the basis for our recommendation that strain NRRL B-3381 should be the type strain of a new taxon, for which we propose the name Aeromicrobium erythreum.     

大连地区海泥样品中分离的五株海洋放线菌的研究

对从大连小平岛地区海面下10~20 m处的海泥样品中分离的5株海洋放线菌进行了生理特征和抗菌活性的研究。抗菌活性实验初步表明,菌株S097,S187和S233具有较好的拮抗革兰氏阳性菌、革兰氏阴性菌和真菌测试菌株的活性,尤其是菌株S233对绿脓杆菌和白色假丝酵母的抑制活性很强。16 s rDNA序列分析结果表明,5株放线菌(S097,S187,S233,S239,L180)分别与Streptomyces argenteolusCGMCC 4.1693、S.flavofuscusNRRL B-8036、S.variabilisNRRL B-3984T、S.lit-m ocidiniNRRL B-3635和S.sulphureusNRRL B-1627T显示出最高的序列同源性(99%),这是这些菌种首次报道在大连地区的海泥样品中得到分离。利用I型聚酮合成酶(PKSI)兼并引物从菌株S187中扩增出了PKSI片段,揭示了该菌株生产I型聚酮类化合物的潜在能力。本文的研究结果为进一步开发利用大连地区海泥中的海洋放线菌资源奠定了基础。     

1-Ene-steroid reductase of Mycobacterium sp. NRRL B-3805

The microbial enzymatic reduction of 1,4-androstadiene-3,17-dione (ADD) to 4-androstene-3,17-dione (AD), testosterone and 1-dehydrotestosterone (DHT) is described. Two reducing activities observed in washed cell suspensions and cell free extracts of Mycobacterium sp. NRRL B-3805 were found to account for these bioconversions. One was a 1-ene-steroid reductase and the other a 17-keto steroid reductase. The first reducing activity was found to appear in the soluble cell fraction whereas the latter could be precipitated by centrifugation. Maximum 1-ene-steroid reductase specific activity was achieved during the exponential growth phase of the organism and significantly increased upon induction with ADD. The 1-ene-steroid reductase was partially purified (30-fold) by ammonium sulfate fractionation, gel-filtration and ion-exchange chromatography, and was eluted from a Sephacryl S-300 column with an Mr = 115,000. The 1-ene-steroid reductase activity was NADPH-dependent and had specificity towards steroid compounds containing C-1,2 double bond with an apparent Km for ADD of 2.2 X 10(-5) M. The reverse reaction catalyzing C-1,2 dehydrogenation could not be detected in our preparations. The results suggest that in Mycobacterium sp NRRL B-3805 and B-3683 the steroid C-1,2 dehydrogenation and 1-ene reduction are two separable activities.     

Microbial Oxidation of Hydrocarbons and Related Compounds by Whole-Cell Suspensions of the Methane-Oxidizing Bacterium H-2

Previously, a thermophilic obligate methane-oxidizing bacterium, H-2 (type I), was isolated in our laboratory. H-2 is a new type of methylotroph because of the G+C content of DNA; it uses both the ribulose monophosphate pathway and the serine pathway for carbon assimilation and possesses a new quinone. In addition, we found that resting cell suspensions of H-2 had the ability to oxidize a variety of compounds different from the other methane-oxidizing bacteria as follows. (i) C₁ to C₈n-alkanes are hydroxylated and further oxidized, yielding mixtures of the corresponding alcohols, aldehydes, acids, and ketones. Liquid alkanes are transformed through a different oxidative pathway from that of gaseous ones. (ii) Both gaseous (C₂ to C₄) and liquid (C₅, C₆) n-alkenes are oxidized to their corresponding 1,2-epoxides. (iii) Liquid monochloro and dichloro n-alkanes (C₅, C₆) are oxidized, yielding their corresponding acids or haloacids. (iv) Diethyl ether is oxidized to acetic acid; no ethanol and acetaldehyde are detected. (v) Cyclic and aromatic compounds are also oxidized. (vi) Secondary alcohols (C₃ to C₁₀) are oxidized to their corresponding methyl ketones.     

The obligatory intermediacy of 16,17 alpha- and 16,17 beta-epoxides in the biotransformation of androsta-5,16-dien-3 beta-ol to androst-5-ene-3 beta, 16 alpha, 17 beta- and -3 beta, 16 beta, 17 alpha-triols by male rat liver microsomes

The C16-double bond of the biolefinic steroid, androsta-5,16-dien-3 beta-ol (delta 16-ANDO), was regioselectively oxidized by male rat liver microsomes in the presence of NADPH and EDTA to 16 alpha, 17 alpha-epoxyandrost-5-en-3 beta-ol (delta 16-ANDO 16,17 alpha-epoxide), 16 beta,-17 beta-epoxyandrost-5-en-3 beta-ol (delta 16-ANDO 16,17 beta-epoxide), androst-5-ene-3 beta, 16 alpha, 17 beta-triol (delta 16-ANDO 16 alpha, 17 beta-glycol), and androst-5-ene-3 beta, 16 beta, 17 alpha-triol (delta 16-ANDO 16 beta, 17 alpha-glycol). The microsomes hydrolyzed delta 16-ANDO 16,17 alpha-epoxide specifically to the 16 beta, 17 alpha-glycol and delta 16-ANDO 16,17 beta-epoxide to the 16 beta, 17 alpha-glycol and the 16 alpha, 17 beta-glycol in an equal ratio. delta 16-ANDO 16,17 alpha-epoxide was much more susceptible to microsomal hydrolysis than the 16,17 beta-epoxide. The xenobiotic epoxide hydrolase inhibitor, 3,3,3-trichloropropene 1,2-oxide, potently inhibited microsomal hydrolysis of delta 16-ANDO 16,17-epoxides as well as of benzo[a]pyrene 4,5-epoxide and styrene 7,8-epoxide. Addition of 3,3,3-trichloropropene 1,2-oxide accumulated the 16,17-epoxides formed from delta 16-ANDO in the reaction medium with concomitant decrease in the amounts of the 16,17-glycols formed, leading to a conclusion that the 16,17-epoxides played a role as obligatory intermediates in the microsomal delta 16-oxidation of delta 16-ANDO to the 16,17-glycols. Epoxidation of delta 16-ANDO was stereoselectively mediated by a cytochrome P-450 with quite unique properties to form the 16,17 alpha-epoxide as the major oxidation product and the 16,17 beta-epoxide as the minor. The epoxidation was strongly inhibited with CO, activated with 2-diethylaminoethyl 2,2-diphenylvalerate hydrochloride more than twice as much, and little affected with metyrapone and 7,8-benzoflavone. A pretreatment of the animals with 3-methylcholanthrene induced the delta 16-ANDO-epoxidizing activity of their microsomes 1.5 times higher than those from the control animals. However, a pretreatment with phenobarbital reduced the enzyme activity to one-half of the control microsomes. Under the same conditions, microsomal activities of hydroxylation of benzo[a]pyrene and N-demethylation of benzphetamine were significantly induced by the pretreatments with 3-methylcholanthrene and phenobarbital, respectively.     

Production of epoxides from gaseous alkenes by resting-cell suspensions and immobilized cells of alkene-utilizing bacteria

Summary Newly isolated and already available strains of alkene-utilizing bacteria were able to oxidize ethene, propene or 1-butene to the respective 1,2-epoxides. Resting-cell suspensions of organisms isolated on propene and butene, when grown on these substrates converted ethene quantitatively to epoxyethane. Some, but not all ethene-utilizing strains accumulated 1,2-epoxypropane or 1,2-epoxybutane when propene or butene was supplied, although not quantitatively because the epoxides produced were partially further metabolized. Suitable epoxide producers which eventually may be employed as biocatalysts in a biotechnological process were used for immobilization in calcium alginate and K-carrageenan; after immobilization, 60%–100% activity for epoxide production was retained.     

Microbiological production of radioisotopically labelled 16 alpha-hydroxylated steroids in trace quantities.

[14-14C]16 alpha-Hydroxy-C-18- and C-19-steroid hormones were obtained in good yields by microbiological hydroxylation of correspondingly labelled steroids by Streptomyces roseochromogenes NRRL B-1233. Trace quantities of the labelled substrates were incubated on a rotary shaker (220 rpm) at 27 degrees C. The radioactive products were chromatographically separated, identified and the radiochemical purity was established by isotopic dilution analysis. The specific activities of 16 alpha-hydroxy-steroids obtained were assumed to be the same as those of the substrates, namely, 57.5 mCi/mmole for 16 alpha-hydroxy-4-androstene-3,17-dione, 57.5 mCi/mmole for 5-androstene-3 beta,16 alpha,17 beta-triol, 57.5 mCi/mmole for 16 alpha-hydroxy-dehydroepiandrosterone, 55.7 mCi/mmole for 16 alpha-hydroxy-estrone, and 57.5 mCi/mmole for 16 alpha-hydroxy-testosterone.     

Comprehensive analysis of collagen metabolism in vitro using [4(3H)]/[14C]proline dual-labeling and polyacrylamide gel electrophoresis

A method to simultaneously quantify the production, secretion, and prolyl hydroxylation of individual types of collagen in cell culture samples has been developed. Collagens were biosynthetically labeled with a mixture of [14C]proline and [4-3H]proline. The labeled collagens were isolated and their component alpha-chains were resolved by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Migration of the collagen alpha-chains was determined by fluorography, and radioactivity in excised bands was quantified by scintillation counting. [14C]Proline labeling of collagen chains was used to determine the production and secretion of the different types of collagen. The ratios of the component alpha 1(I) and alpha 2(I) chains of type I collagen were also determined in this way. Prolyl hydroxylation of collagen alpha-chains was readily determined by measurement of their 3H:14C ratios. Following 4-hydroxylation, 3H was lost from the [4-3H]proline with alteration of this ratio. This dual-labeling method is suitable for the comprehensive analysis of collagen metabolism in multiple samples.     

Complete genome sequence of Lactobacillus buchneri NRRL B-30929, a novel strain from a commercial ethanol plant

Lactobacillus buchneri strain NRRL B-30929 was a contaminant obtained from a commercial ethanol fermentation. This facultative anaerobe is unique because of its rapid growth on xylose and simultaneous fermentation of xylose and glucose. The strain utilizes a broad range of carbohydrate substrates and possesses a high tolerance to ethanol and other stresses, making it an attractive candidate for bioconversion of biomass substrates to various bioproducts. The genome sequence of NRRL B-30929 will provide insight into the unique properties of this lactic acid bacterium.     

Physiological meaning and potential for application of reductive dechlorination by anaerobic bacteria

Abstract: The physiological meaning of reductive dechlorination reactions catalyzed by anaerobic bacteria can be explained as a co-metabolic activity or as a novel type of respiration. Co-metabolic activities have been found mainly with alkyl halides. They are non-specific reactions catalyzed by various enzyme systems of facultative as well as obligate anaerobic bacteria. In contrast, the reductive dechlorinations involved in metabolic respiration processes are very specific reactions. Only a limited number of alkyl and aryl chlorinated compounds is presently known to function as a terminal electron acceptor in a few, recently isolated bacteria. Metabolic dechlorination rates are in general several orders of magnitude higher than co-metabolic ones. Both reaction types are suitable for the anaerobic treatment of waste streams.