title: Metabolism of dichloromethylcatechols as central intermediates in the degradation of dichlorotoluenes by Ralstonia sp. strain PS12.
abstract: Ralstonia sp. strain PS12 is able to use 2,4-, 2,5-, and 3,4-dichlorotoluene as growth substrates. Dichloromethylcatechols are central intermediates that are formed by TecA tetrachlorobenzene dioxygenase-mediated activation at two adjacent unsubstituted carbon atoms followed by TecB chlorobenzene dihydrodiol dehydrogenase-catalyzed rearomatization and then are channeled into a chlorocatechol ortho cleavage pathway involving a chlorocatechol 1,2-dioxygenase, chloromuconate cycloisomerase, and dienelactone hydrolase. However, completely different metabolic routes were observed for the three dichloromethylcatechols analyzed. Whereas 3,4-dichloro-6-methylcatechol is quantitatively transformed into one dienelactone (5-chloro-2-methyldienelactone) and thus is degraded via a linear pathway, 3,5-dichloro-2-methylmuconate formed from 4,6-dichloro-3-methylcatechol is subject to both 1,4- and 3,6-cycloisomerization and thus is degraded via a branched metabolic route. 3,6-Dichloro-4-methylcatechol, on the first view, is transformed predominantly into one (2-chloro-3-methyl-trans-) dienelactone. In situ (1)H nuclear magnetic resonance analysis revealed the intermediate formation of 2,5-dichloro-4-methylmuconolactone, showing that both 1,4- and 3,6-cycloisomerization occur with this muconate and indicating a degradation of the muconolactone via a reversible cycloisomerization reaction and the dienelactone-forming branch of the pathway. Diastereomeric mixtures of two dichloromethylmuconolactones were prepared chemically to proof such a hypothesis. Chloromuconate cycloisomerase transformed 3,5-dichloro-2-methylmuconolactone into a mixture of 2-chloro-5-methyl-cis- and 3-chloro-2-methyldienelactone, affording evidence for a metabolic route of 3,5-dichloro-2-methylmuconolactone via 3,5-dichloro-2-methylmuconate into 2-chloro-5-methyl-cis-dienelactone. 2,5-Dichloro-3-methylmuconolactone was transformed nearly exclusively into 2-chloro-3-methyl-trans-dienelactone.
authors.affiliation: Department of Environmental Microbiology, GBF-German Research Center for Biotechnology, D-38124 Braunschweig. Chemical Microbiology, Bergische University, Wuppertal, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Pollmann
authors.forename: Stefan
authors.initials: S
authors.lastname: Kaschabek
authors.forename: Victor
authors.initials: V
authors.lastname: Wray
authors.forename: Walter
authors.initials: W
authors.lastname: Reineke
authors.forename: Dietmar H
authors.initials: DH
authors.lastname: Pieper
mesh_terms: D020562:Betaproteobacteria / Q000254:growth & development / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002396:Catechols / Q000737:chemistry* / Q000378:metabolism*; D019753:Intramolecular Lyases / Q000378:metabolism; D007783:Lactones / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D013011:Sorbic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D014050:Toluene / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002396:Catechols; D007783:Lactones; D014050:Toluene; C005939:muconic acid; C056009:2,4-dichlorotoluene; C039879:muconolactone; D019753:Intramolecular Lyases; C055773:chloromuconate cycloisomerase; D013011:Sorbic Acid