Microorganisms degrading chlorobenzene via a meta-cleavage pathway harbor highly similar chlorocatechol 2,3-dioxygenase-encoding gene clusters. Arch Microbiol 182: 147-156
Chemische Mikrobiologie, Bergische Universität Wuppertal, Fachbereich C, Gaubetastrabetae 20, 42097 Wuppertal, Germany. Archives of Microbiology
(Impact Factor: 1.67).
11/2004; 182(2-3):147-56. DOI: 10.1007/s00203-004-0681-5
Pseudomonas putida GJ31 harbors a degradative pathway for chlorobenzene via meta-cleavage of 3-chlorocatechol. Pseudomonads using this route for chlorobenzene degradation, which was previously thought to be generally unproductive, were isolated from various contaminated environments of distant locations. The new isolates, Pseudomonas fluorescens SK1 (DSM16274), Pseudomonas veronii 16-6A (DSM16273), Pseudomonas sp. strain MG61 (DSM16272), harbor a chlorocatechol 2,3-dioxygenase (CbzE). The cbzE-like genes were cloned, sequenced, and expressed from the isolates and a mixed culture. The chlorocatechol 2,3-dioxygenases shared 97% identical amino acids with CbzE from strain GJ31, forming a distinct family of catechol 2,3-dioxygenases. The chlorocatechol 2,3-dioxygenase, purified from chlorobenzene-grown cells of strain SK1, showed an identical N-terminal sequence with the amino acid sequence deduced from cloned cbzE. In all investigated chlorobenzene-degrading strains, cbzT-like genes encoding ferredoxins are located upstream of cbzE. The sequence data indicate that the ferredoxins are identical (one amino acid difference in CbzT of strain 16-6A compared to the others). In addition, the structure of the operon downstream of cbzE is identical in strains GJ31, 16-6A, and SK1 with genes cbzX (unknown function) and the known part of cbzG (2-hydroxymuconic semialdehyde dehydrogenase) and share 100% nucleotide sequence identity with the entire downstream region. The current study suggests that meta-cleavage of 3-chlorocatechol is not an atypical pathway for the degradation of chlorobenzene.
Available from: Raghunath Satpathy
- "Consequently, 2-haloalkanoic acid dehalogenase may be worthy for its bioremediation mechanism for different haloacid pollutants. Many microorganisms can break down halogenated compounds by cleaving their carbon-halogen bonds via dehalogenase-catalyzed reactions and, therefore, may aid in the removal of organohalides pollutant from the environment   . These dehalogenase enzymes are broadly classified as haloalkane dehalogenases, halohydrin dehalogenases, haloacetate dehalogenases, dichloromethane dehalogenases, and D-and L-haloalkanoic acid dehalogenases based on their cleavage nature  . "
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ABSTRACT: 2-Haloalkanoic acid dehalogenase enzymes have broad range of applications, starting from bioremediation to chemical synthesis of useful compounds that are widely distributed in fungi and bacteria. In the present study, a total of 81 full-length protein sequences of 2-haloalkanoic acid dehalogenase from bacteria and fungi were retrieved from NCBI database. Sequence analysis such as multiple sequence alignment (MSA), conserved motif identification, computation of amino acid composition, and phylogenetic tree construction were performed on these primary sequences. From MSA analysis, it was observed that the sequences share conserved lysine (K) and aspartate (D) residues in them. Also, phylogenetic tree indicated a subcluster comprised of both fungal and bacterial species. Due to nonavailability of experimental 3D structure for fungal 2-haloalkanoic acid dehalogenase in the PDB, molecular modelling study was performed for both fungal and bacterial sources of enzymes present in the subcluster. Further structural analysis revealed a common evolutionary topology shared between both fungal and bacterial enzymes. Studies on the buried amino acids showed highly conserved Leu and Ser in the core, despite variation in their amino acid percentage. Additionally, a surface exposed tryptophan was conserved in all of these selected models.
Available from: Pankaj Kumar Arora
- "This pathway has been demonstrated in several other strains that are able to metabolize 3CC, including Pseudomonas sp. MG61, Pseudomonas fluorescens SK1 and Pseudomonas veronii 16-6A . "
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ABSTRACT: Chlorophenols (CPs) and their derivatives are persistent environmental pollutants which are used in the manufacture of dyes, drugs, pesticides and other industrial products. CPs, which include monochlorophenols, polychlorophenols, chloronitrophenols, chloroaminophenols and chloromethylphenols, are highly toxic to living beings due to their carcinogenic, mutagenic and cytotoxic properties. Several physico-chemical and biological methods have been used for removal of CPs from the environment. Bacterial degradation has been considered a cost-effective and eco-friendly method of removing CPs from the environment. Several bacteria that use CPs as their sole carbon and energy sources have been isolated and characterized. Additionally, the metabolic pathways for degradation of CPs have been studied in bacteria and the genes and enzymes involved in the degradation of various CPs have been identified and characterized. This review describes the biochemical and genetic basis of the degradation of CPs and their derivatives.
Available from: archives-ouvertes.fr
- "The gene encoding this dioxygenase (cbzE) is preceded by a xylT-like gene called cbzT. The same is true for other chlorobenzene-degrading strains using the meta-cleavage pathway (Göbel et al., 2004). The CbzE enzyme was found to undergo inactivation during catalysis of 4-methylcatechol cleavage, suggesting that the loss of activity resulted from an oxidation of the active site iron as shown for C23O mt-2 . "
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ABSTRACT: Extradiol dioxygenases are ubiquitous enzymes that catalyze ring cleavage of a wide variety of aromatic compounds. Most of these enzymes contain a ferrous ion at the active site, which is bound to the polypeptide chain through a conserved triad of two histidines and one glutamic acid. During the catalytic cycle, a catecholic substrate first binds at the active site, followed by dioxygen and the ternary complex formed yields a bound superoxide that attacks the substrate, leading eventually to ring cleavage. The active site iron remains ferrous during catalysis, except when poor substrates such as chloro- or methylcatechols are processed. In such cases, the enzyme becomes inactivated through oxidation and eventually loss of its active site iron atom. In Pseudomonas putida mt-2, catechol 2,3-dioxygenase, which is involved in toluene degradation, is inactivated by 4-methylcatechol. The enzyme is however rescued by a specific reactivation system involving a [2Fe-2S] ferredoxin encoded by xylT. The role of this ferredoxin is to reduce the ferric ion of the inactive enzyme thereby regenerating the active catalyst. Recent findings indicate that the electrons needed for the XylT-mediated reactivation are provided by XylZ, a NADH-oxidoreductase that is part of the toluate dioxygenase complex. XylT analogues present in other bacteria have been shown to have a similar role in the reactivation of catechol dioxygenases involved in the degradation of various aromatic hydrocarbons including cresols, chlorobenzene and naphthalene. The occurrence and significance of ferredoxin-mediated extradiol dioxygenae repair systems in bacteria is discussed.
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