title: Regulator and enzyme specificities of the TOL plasmid-encoded upper pathway for degradation of aromatic hydrocarbons and expansion of the substrate range of the pathway.
abstract: The TOL plasmid upper pathway operon encodes enzymes involved in the catabolism of aromatic hydrocarbons such as toluene and xylenes. The regulator of the gene pathway, the XylR protein, exhibits a very broad effector specificity, being able to recognize as effectors not only pathway substrates but also a wide variety of mono- and disubstituted methyl-, ethyl-, and chlorotoluenes, benzyl alcohols, and p-chlorobenzaldehyde. Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase, two upper pathway enzymes, exhibit very broad substrate specificities and transform unsubstituted substrates and m- and p-methyl-, m- and p-ethyl-, and m- and p-chloro-substituted benzyl alcohols and benzaldehydes, respectively, at a high rate. In contrast, toluene oxidase only oxidizes toluene, m- and p-xylene, m-ethyltoluene, and 1,2,4-trimethylbenzene [corrected], also at a high rate. A biological test showed that toluene oxidase attacks m- and p-chlorotoluene, albeit at a low rate. No evidence for the transformation of p-ethyltoluene by toluene oxidase has been found. Hence, toluene oxidase acts as the bottleneck step for the catabolism of p-ethyl- and m- and p-chlorotoluene through the TOL upper pathway. A mutant toluene oxidase able to transform p-ethyltoluene was isolated, and a mutant strain capable of fully degrading p-ethyltoluene was constructed with a modified TOL plasmid meta-cleavage pathway able to mineralize p-ethylbenzoate. By transfer of a TOL plasmid into Pseudomonas sp. strain B13, a clone able to slowly degrade m-chlorotoluene was also obtained.
authors.affiliation: Estación Experimental del Zaidin, Consejo Superior de Investigaciones Cientificas, Granada, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Abril
authors.forename: C
authors.initials: C
authors.lastname: Michan
authors.forename: K N
authors.initials: KN
authors.lastname: Timmis
authors.forename: J L
authors.initials: JL
authors.lastname: Ramos
mesh_terms: D004790:Enzyme Induction; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics*; D005798:Genes, Bacterial; D005809:Genes, Regulator; D006838:Hydrocarbons / Q000378:metabolism*; D007700:Kinetics; D009876:Operon; D010957:Plasmids; D011549:Pseudomonas / Q000201:enzymology / Q000235:genetics*; D013379:Substrate Specificity; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D029968:Escherichia coli Proteins; D006838:Hydrocarbons; D014157:Transcription Factors; C579718:XylR protein, E coli