Degradation of Benzene by Pseudomonas veronii 1YdBTEX2 and 1YB2 Is Catalyzed by Enzymes Encoded in Distinct Catabolism Gene Clusters

Abstract

Pseudomonas veronii 1YdBTEX2, a benzene and toluene degrader, and Pseudomonas veronii 1YB2, a benzene degrader, have previously been shown to be key players in a benzene-contaminated site. These strains harbor unique catabolic pathways for the degradation of benzene comprising a gene cluster encoding an isopropylbenzene dioxygenase where genes encoding downstream enzymes were interrupted by stop codons. Extradiol dioxygenases were recruited from gene clusters comprising genes encoding a 2-hydroxymuconic semialdehyde dehydrogenase necessary for benzene degradation but typically absent from isopropylbenzene dioxygenase-encoding gene clusters. The benzene dihydrodiol dehydrogenase-encoding gene was not clustered with any other aromatic degradation genes, and the encoded protein was only distantly related to dehydrogenases of aromatic degradation pathways. The involvement of the different gene clusters in the degradation pathways was suggested by real-time quantitative reverse transcription PCR.

The Genome of the Toluene-Degrading Pseudomonas veronii Strain 1YdBTEX2 and Its Differential Gene Expression in Contaminated Sand

“…veronii strain 1YdBTEX2 is mostly known for its capacity to degrade aromatic solvents such as BTEX [15, 16, 49]. Toluene and benzene are degraded through the same catabolic pathway but the enzymes potentially catalyzing these reactions are encoded in at least three to four gene clusters, several of which seem redundant [49].…”

“…veronii strain 1YdBTEX2 is mostly known for its capacity to degrade aromatic solvents such as BTEX [15, 16, 49]. Toluene and benzene are degraded through the same catabolic pathway but the enzymes potentially catalyzing these reactions are encoded in at least three to four gene clusters, several of which seem redundant [49]. Degradation of BTEX is thought to proceed via a multi-component aromatic ring dioxygenase, followed by a benzene-dihydrodiol dehydrogenase yielding catechol intermediates, and a meta -cleavage pathway, finally producing acetyl-CoA (Fig 4D) [49].…”

“…Toluene and benzene are degraded through the same catabolic pathway but the enzymes potentially catalyzing these reactions are encoded in at least three to four gene clusters, several of which seem redundant [49]. Degradation of BTEX is thought to proceed via a multi-component aromatic ring dioxygenase, followed by a benzene-dihydrodiol dehydrogenase yielding catechol intermediates, and a meta -cleavage pathway, finally producing acetyl-CoA (Fig 4D) [49]. One of the involved gene clusters ( ipbAaAbAcAdBCEGFHD ) is localized on chromosome 2 (Fig 1B, Fig 4A), and includes both the genes for the aromatic ring dioxygenase ( ipbAaAbAcAd ) and a set of meta- cleavage pathway genes ( ipbCEGFHD ).…”

“…A clear exception was the gene for the putative alternative benzene-dihydrodiol dehydrogenase (PVE_r2g0805), whose expression was unaffected by the change from succinate to toluene (Fig 6, compare Li-Su with Sa-To). This gene (PVE_r2g0805) has previously been proposed to be recruited and to replace the interrupted ipbB gene within the ipb operon [18, 49, 50]. Multiple redundant genes encoding parts of meta -cleavage pathways for catechol metabolism are induced upon exposure to toluene.…”

“…The gene for dihydrodiol dehydrogenase ( ipbB ) is inactivated by two non-sense mutations and is preceded by a transposon insertion (Fig 4A). The dihydrodiol dehydrogenase function in toluene degradation is most likely complemented by the constitutively expressed gene PVE_r2g0805 (Fig 7C) [49]. Curiously, three a priori redundant meta- cleavage pathways are encoded on chromosome 2, the first similar to an archetype dmp phenol pathway, the second part of the ipb pathway and the third similar to a pathway from naphthalene/salicylate degradation (Fig 4).…”