ferredoxins, three meta-cleavage enzymes. The genes encoding these enzymes are
dispersed among several gene clusters. Similar findings have been observed in case
of Sphingomonas aromaticivorans F199 as well (Romine et al. 1999) that contain
several oxygenase subunits an important characteristic of Sphingomonas sp. Furthermore, the gene products can combine in a random fashion to form hybrid
aromatic oxygenase. So far, there is lack of information on several groups of
isoenzymes of strain RW1 (Sphingomonas sp.). They might play an important role
in different metabolic pathways.
The RW1 (Sphingomonas sp.) can use dioxin and DF as a sole carbon source;
however, it cannot grow on chlorinated dioxins and DF. It could be due to limited
substrate range of initial dioxin dioxygenase, formation of dead end products and
toxic intermediates. 3-chlorocatechol, the intermediate formed has been found to
inhibit extradiol ring-cleavage dioxygenases (Bartels et al. 1984). Catechol 2,3dioxygenase from Pseudomonas putida mt-2 is the best example where the mechanism of inhibition has been studied (Bartels et al. 1984).
Genetic structure of catabolic genes involved in DF degradation of CA10 (P.
resonvorans) has been also well characterized. Upstream flanking region of carBC
gene of CA10 has two ORFs (ORF4 and ORF5). Similarly, downstream region of
carBC gene has three ORFs (ORF6, ORF7 and ORF8). When sequenced, ORF6
demonstrated homology with ferredoxin and ORF8 showed homology with ferredoxin reductase component of bacterial multicomponent dioxygenase system. ORF4
and ORF5 share sequence homology and the amino acid sequence demonstrated
approximately 30% homology with alpha subunit (large subunit) of terminal
oxygenase component.
ORF4 and ORF-5 (product-terminal dioxygenase), ORF6 (product-ferredoxin)
and ORF8 (product-ferredoxin reductase) of CARDO (carbazole 1,9a-dioxygenase)
attack the angular position adjacent to the nitrogen atom of carbazole. However, the
product of ORF7 is not indispensable for CARDO activity. Hence, ORF4, ORF5,
ORF6 and ORF8 were designated as carAa, carAb, carAc and carAd, respectively.
The products of carAa (ORF4), ORF7 and carAd (ORF8) have a molecular
weight of 43, 36 and 11 kDa, respectively as revealed by SDS-PAGE. However,
the product of carAc was not visible on SDS-PAGE. CARDO can oxidize several
polyaromatic compounds that include DD, DF, biphenyl and polycyclic aromatic
hydrocarbons (naphthalene and phenanthrene). DD and DF form 2,2
0 ,3trihydroxydiphenyl ether and 2,2
0 ,3-trihydroxybiphenyl metabolites and thus it has
been concluded that CARDO attacks at the angular position is adjacent to the oxygen
atom of DD and DF similar to carbazole (Nojiri and Omori 2002).
The genes dbfA1A2 (oxygenase component of multicomponent dioxygenase),
dbfBC (meta-cleavage enzyme and hydrolase) and pht (phthalate-degrading
enzymes) of strain DBF63 (Terrabacter sp.) clearly reveal an important role in
aromatic compound degradation. The DBF63 cells when grown on DF and/or
fluorene clearly demonstrated that the DbfA1A2 and DbfBC are responsible for
catalysing the conversion of DF to salicylate and both DbfA1A2 and Pht enzymes
are involved in degradation of fluorene. In vitro experiments have confirmed that
dbfA1A2 cistron and pht operon are located on pDBF1–160 kb and pDBF2–190 kb
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P. K. Jaiswal and J. Gupta
dispersed among several gene clusters. Similar findings have been observed in case
of Sphingomonas aromaticivorans F199 as well (Romine et al. 1999) that contain
several oxygenase subunits an important characteristic of Sphingomonas sp. Furthermore, the gene products can combine in a random fashion to form hybrid
aromatic oxygenase. So far, there is lack of information on several groups of
isoenzymes of strain RW1 (Sphingomonas sp.). They might play an important role
in different metabolic pathways.
The RW1 (Sphingomonas sp.) can use dioxin and DF as a sole carbon source;
however, it cannot grow on chlorinated dioxins and DF. It could be due to limited
substrate range of initial dioxin dioxygenase, formation of dead end products and
toxic intermediates. 3-chlorocatechol, the intermediate formed has been found to
inhibit extradiol ring-cleavage dioxygenases (Bartels et al. 1984). Catechol 2,3dioxygenase from Pseudomonas putida mt-2 is the best example where the mechanism of inhibition has been studied (Bartels et al. 1984).
Genetic structure of catabolic genes involved in DF degradation of CA10 (P.
resonvorans) has been also well characterized. Upstream flanking region of carBC
gene of CA10 has two ORFs (ORF4 and ORF5). Similarly, downstream region of
carBC gene has three ORFs (ORF6, ORF7 and ORF8). When sequenced, ORF6
demonstrated homology with ferredoxin and ORF8 showed homology with ferredoxin reductase component of bacterial multicomponent dioxygenase system. ORF4
and ORF5 share sequence homology and the amino acid sequence demonstrated
approximately 30% homology with alpha subunit (large subunit) of terminal
oxygenase component.
ORF4 and ORF-5 (product-terminal dioxygenase), ORF6 (product-ferredoxin)
and ORF8 (product-ferredoxin reductase) of CARDO (carbazole 1,9a-dioxygenase)
attack the angular position adjacent to the nitrogen atom of carbazole. However, the
product of ORF7 is not indispensable for CARDO activity. Hence, ORF4, ORF5,
ORF6 and ORF8 were designated as carAa, carAb, carAc and carAd, respectively.
The products of carAa (ORF4), ORF7 and carAd (ORF8) have a molecular
weight of 43, 36 and 11 kDa, respectively as revealed by SDS-PAGE. However,
the product of carAc was not visible on SDS-PAGE. CARDO can oxidize several
polyaromatic compounds that include DD, DF, biphenyl and polycyclic aromatic
hydrocarbons (naphthalene and phenanthrene). DD and DF form 2,2
0 ,3trihydroxydiphenyl ether and 2,2
0 ,3-trihydroxybiphenyl metabolites and thus it has
been concluded that CARDO attacks at the angular position is adjacent to the oxygen
atom of DD and DF similar to carbazole (Nojiri and Omori 2002).
The genes dbfA1A2 (oxygenase component of multicomponent dioxygenase),
dbfBC (meta-cleavage enzyme and hydrolase) and pht (phthalate-degrading
enzymes) of strain DBF63 (Terrabacter sp.) clearly reveal an important role in
aromatic compound degradation. The DBF63 cells when grown on DF and/or
fluorene clearly demonstrated that the DbfA1A2 and DbfBC are responsible for
catalysing the conversion of DF to salicylate and both DbfA1A2 and Pht enzymes
are involved in degradation of fluorene. In vitro experiments have confirmed that
dbfA1A2 cistron and pht operon are located on pDBF1–160 kb and pDBF2–190 kb
304
P. K. Jaiswal and J. Gupta