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1.
The initial activation reactions of anaerobic oxidation of the aromatic hydrocarbons toluene and ethylbenzene were investigated in cell extracts of a toluene-degrading, sulfate-reducing bacterium, Desulfobacula toluolica, and in cell extracts of strain EbN1, a denitrifying bacterium capable of degrading toluene and ethylbenzene. Extracts of toluene-grown cells of both species catalysed the addition of fumarate to the methyl group of [phenyl-14C]-toluene and formed [14C]-labeled benzylsuccinate. Extracts of ethylbenzene-grown cells of strain EbN1 did not catalyse this reaction, but catalysed the formation of 1-phenylethanol and acetophenone from [methylene-14C]-ethylbenzene. Toluene-grown cells of D. toluolica and strain EbN1 synthesised highly induced polypeptides corresponding to the large subunits of benzylsuccinate synthase from Thauera aromatica. These polypeptides were absent in strain EbN1 after growth on ethylbenzene, although a number of different polypeptides were highly induced. Thus, formation of benzylsuccinate from toluene and fumarate appears to be the general initiating step in anaerobic toluene degradation by bacteria affiliated with the phylogenetically distinct β-subclass (strain EbN1 and T. aromatica) and δ-subclass (D. toluolica) of the Proteobacteria. Anaerobic ethylbenzene oxidation proceeds via a different pathway involving a two-step oxidation of the methylene group to an alcohol and an oxo group; these steps are most probably followed by a biotin-independent carboxylation reaction and thiolytic cleavage. Received: 16 March 1998 / Accepted: 27 June 1998  相似文献   

2.
Anaerobic degradation of the aromatic hydrocarbon ethylbenzene was studied with sulfate as the electron acceptor. Enrichment cultures prepared with marine sediment samples from different locations showed ethylbenzene-dependent reduction of sulfate to sulfide and always contained a characteristic cell type that formed gas vesicles towards the end of growth. A pure culture of this cell type, strain EbS7, was isolated from sediment from Guaymas Basin (Gulf of California). Complete mineralization of ethylbenzene coupled to sulfate reduction was demonstrated in growth experiments with strain EbS7. Sequence analysis of the 16S rRNA gene revealed a close relationship between strain EbS7 and the previously described marine sulfate-reducing strains NaphS2 and mXyS1 (similarity values, 97.6 and 96.2%, respectively), which grow anaerobically with naphthalene and m-xylene, respectively. However, strain EbS7 did not oxidize naphthalene, m-xylene, or toluene. Other compounds utilized by strain EbS7 were phenylacetate, 3-phenylpropionate, formate, n-hexanoate, lactate, and pyruvate. 1-Phenylethanol and acetophenone, the characteristic intermediates in anaerobic ethylbenzene degradation by denitrifying bacteria, neither served as growth substrates nor were detectable as metabolites by gas chromatography-mass spectrometry in ethylbenzene-grown cultures of strain EbS7. Rather, (1-phenylethyl)succinate and 4-phenylpentanoate were detected as specific metabolites in such cultures. Formation of these intermediates can be explained by a reaction sequence involving addition of the benzyl carbon atom of ethylbenzene to fumarate, carbon skeleton rearrangement of the succinate moiety (as a thioester), and loss of one carboxyl group. Such reactions are analogous to those suggested for anaerobic n-alkane degradation and thus differ from the initial reactions in anaerobic ethylbenzene degradation by denitrifying bacteria which employ dehydrogenations.  相似文献   

3.
Rhodococcus sp. strain DK17 was isolated from soil and analyzed for the ability to grow on o-xylene as the sole carbon and energy source. Although DK17 cannot grow on m- and p-xylene, it is capable of growth on benzene, phenol, toluene, ethylbenzene, isopropylbenzene, and other alkylbenzene isomers. One UV-generated mutant strain, DK176, simultaneously lost the ability to grow on o-xylene, ethylbenzene, isopropylbenzene, toluene, and benzene, although it could still grow on phenol. The mutant strain was also unable to oxidize indole to indigo following growth in the presence of o-xylene. This observation suggests the loss of an oxygenase that is involved in the initial oxidation of the (alkyl)benzenes tested. Another mutant strain, DK180, isolated for the inability to grow on o-xylene, retained the ability to grow on benzene but was unable to grow on alkylbenzenes due to loss of a meta-cleavage dioxygenase needed for metabolism of methyl-substituted catechols. Further experiments showed that DK180 as well as the wild-type strain DK17 have an ortho-cleavage pathway which is specifically induced by benzene but not by o-xylene. These results indicate that DK17 possesses two different ring-cleavage pathways for the degradation of aromatic compounds, although the initial oxidation reactions may be catalyzed by a common oxygenase. Gas chromatography-mass spectrometry and 300-MHz proton nuclear magnetic resonance spectrometry clearly show that DK180 accumulates 3,4-dimethylcatechol from o-xylene and both 3- and 4-methylcatechol from toluene. This means that there are two initial routes of oxidation of toluene by the strain. Pulsed-field gel electrophoresis analysis demonstrated the presence of two large megaplasmids in the wild-type strain DK17, one of which (pDK2) was lost in the mutant strain DK176. Since several other independently derived mutant strains unable to grow on alkylbenzenes are also missing pDK2, the genes encoding the initial steps in alkylbenzene metabolism (but not phenol metabolism) appear to be present on this approximately 330-kb plasmid.  相似文献   

4.
5.
Nitrate-reducing bacteria of the recently recognized Azoarcus/Thauera group within the Betaproteobacteria contribute significantly to the biodegradation of aromatic and other refractory compounds in anoxic waters and soils. Strain EbN1 belongs to a distinct cluster (new genus) and is the first member of this phylogenetic group, the genome of which has been determined (4.7 Mb; one chromosome, two plasmids) by [Rabus R, Kube M, Heider J, Beck A, Heitmann K, Widdel F, Reinhardt R (2005) The genome sequence of an anaerobic aromatic-degrading denitrifying bacterium, strain EbN1. Arch Microbiol 183:27–36]. Ten anaerobic and four aerobic aromatic-degradation pathways were recognized on the chromosome, with the coding genes mostly forming clusters. Presence of paralogous gene clusters (e.g. for anaerobic ethylbenzene degradation) suggests an even broader degradation spectrum than previously known. Metabolic versatility is also reflected by the presence of multiple respiratory complexes and is apparently controlled by an extensive regulatory network. Strain EbN1 is unique for its capacity to degrade toluene and ethylbenzene anaerobically via completely different pathways. Bioinformatical analysis of their genetic blueprints and global expression analysis (DNA-microarray and proteomics) of substrate-adapted cells [Kühner S, Wöhlbrand L, Fritz I, Wruck W, Hultschig C, Hufnagel P, Kube M, Reinhardt R, Rabus R (2005) Substrate-dependent regulation of anaerobic degradation pathways for toluene and ethylbenzene in a denitrifying bacterium, strain EbN1. J Bacteriol 187:1493–1503] indicated coordinated vs sequential modes of regulation for the toluene and ethylbenzene pathways, respectively.  相似文献   

6.
A co-culture of two Pseudomonas putida isolates was enriched from sediment on a mixture of benzene, toluene, ethylbenzene, m-xylene, p-xylene, and o-xylene. The co-culture readily degraded each of the compounds present. Benzene, toluene, and ethylbenzene were used as growth substrates by one isolate, while toluene, m-xylene, and p-xylene were used as growth substrates by the other. Neither isolate could grow on o-xylene, but it was removed in the presence of the other compounds presumably by co-metabolism. The findings presented here support other reports in which constructed communities were effectively used to degrade blends of between two and four of the components of BTEX. However, here the co-culture of two P. putida isolates effectively degraded a complete BTEX stream containing all six of the components. Received: 4 September 2001 / Accepted: 19 October 2001  相似文献   

7.
The capability of nitrate-reducing bacteria to degrade alkyltoluenes in the absence of molecular oxygen was investigated with the three isomers of xylene, ethyltoluene, and isopropyltoluene (cymene) in enrichment cultures inoculated with freshwater mud. Denitrifying enrichment cultures developed most readily (within 4 weeks) with p-cymene, a natural aromatic hydrocarbon occurring in plants, and with m-xylene (within 6 weeks). Enrichment of denitrifiers that utilized m-ethyltoluene and p-ethyltoluene was slow (within 8 and 12 weeks, respectively); no enrichment cultures were obtained with the other alkylbenzenes within 6 months. Anaerobic degradation of p-cymene, which has not been reported before, was studied in more detail. Two new types of denitrifying bacteria with oval cells, strains pCyN1 and pCyN2, were isolated; they grew on p-cymene (diluted in an inert carrier phase) and nitrate with doubling times of 12 and 16 h, respectively. Strain pCyN1, but not strain pCyN2, also utilized p-ethyltoluene and toluene. Both strains grew with some alkenoic monoterpenes structurally related to p-cymene, e.g., α-terpinene. In addition, the isolates utilized p-isopropylbenzoate, and mono- and dicarboxylic aliphatic acids. Determination of the degradation balance of p-cymene and growth with acetate and nitrate indicated the capacity for complete oxidation of organic substrates under anoxic conditions. Adaptation studies with cells of strain pCyN1 suggest the existence of at least two enzyme systems for anaerobic alkylbenzene utilization, one metabolizing p-cymene and p-ethyltoluene, and the other metabolizing toluene. Excretion of p-isopropylbenzoate during growth on p-cymene indicated that the methyl group is the site of initial enzymatic attack. Although both strains were facultatively aerobic, as revealed by growth on acetate under air, growth on p-cymene under oxic conditions was observed only with strain pCyN1. Strains pCyN1 and pCyN2 are closely related to members of the Azoarcus-Thauera cluster within the β-subclass of the Proteobacteria, as revealed by 16S rRNA gene sequence analysis. This cluster encompasses several described denitrifiers that oxidize toluene and other alkylbenzenes. Received: 15 July 1998 / Revision received: 29 July 1999 / Accepted: 2 August 1999  相似文献   

8.
Benzene, toluene, ethylbenzene and xylene (BTEX) substrate interactions for a mesophilic (25°C) and thermophilic (50°C) toluene-acclimatized composted pine bark biofilter were investigated. Toluene, benzene, ethylbenzene, o-xylene, m-xylene and p-xylene removal efficiencies, both individually and in paired mixtures with toluene (1:1 ratio), were determined at a total loading rate of 18.1 g m–3 h–1 and retention time ranges of 0.5–3.0 min and 0.6–3.8 min for mesophilic and thermophilic biofilters, respectively. Overall, toluene degradation rates under mesophilic conditions were superior to degradation rates of individual BEX compounds. With the exception of p-xylene, higher removal efficiencies were achieved for individual BEX compounds compared to toluene under thermophilic conditions. Overall BEX compound degradation under mesophilic conditions was ranked as ethylbenzene >benzene >o-xylene >m-xylene >p-xylene. Under thermophilic conditions overall BEX compound degradation was ranked as benzene >o-xylene >ethylbenzene >m-xylene >p-xylene. With the exception of o-xylene, the presence of toluene in paired mixtures with BEX compounds resulted in enhanced removal efficiencies of BEX compounds, under both mesophilic and thermophilic conditions. A substrate interaction index was calculated to compare removal efficiencies at a retention time of 0.8 min (50 s). A reduction in toluene removal efficiencies (negative interaction) in the presence of individual BEX compounds was observed under mesophilic conditions, while enhanced toluene removal efficiency was achieved in the presence of other BEX compounds, with the exception of p-xylene under thermophilic conditions.  相似文献   

9.
A highly enriched denitrifying mixed culture transformedo-xylene cometabolically along with toluene by methyl group oxidation.o-Methyl benzaldehyde ando-methyl benzoic acid accumulated transiently as metabolic products ofo-xylene transformation. Transformation ofo-methyl benzyl alcohol ando-methyl benzaldehyde occurred independently of toluene degradation and resulted in the formation of a compound coeluting witho-methyl benzoic acid on a gas chromatograph. The cometabolic relationship between toluene ando-xylene could be attributed to a mechanism linked to the initial oxidation of the methyl group.  相似文献   

10.
Pseudomonas stutzeri OX1 is able to grow ono-xylene but is unable to grow onm-xylene andp-xylene, which are partially metabolized through theo-xylene degradative pathway leading to the formation of dimethylphenols toxic to OX1.P. stutzeri spontaneous mutants able to grow onm-xylene andp-xylene have been isolated. These mutants soon lose the ability to grow ono-xylene. Data from HPLC analyses and from induction studies suggest that in these mutantsm-xylene andp-xylene could be metabolized through the oxidation of a methyl substituent.P. stutzeri chromosomal DNA is shown to share homology with pWW0 catabolic genes. In the mutant strains the region homologous to pWW0 upper pathway genes has undergone a genomic rearrangement.Abbreviations BADH benzylalcohol dehydrogenase - cat catechol - C23O catechol 2,3-dioxygenase - 2,3-,3,4-,2,4-,2,6-,3,5-2,5-DMP 2,3-,3,4-,2,4-,2,6-,3,5-,2,5-dimethylphenol - 2-MBOH 2-methylbenzyl alcohol - 3-MBOH 3-methylbenzyl alcohol - 4-MBOH 4-methylbenzyl alcohol - m-,p-tol m-,p-toluate - o-,m-,p-xyl o-,m-,p-xylene  相似文献   

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