Metabolism of dichloromethylcatechols as central intermediates in the degradation of dichlorotoluenes by Ralstonia sp. strain PS12

J Bacteriol. 2002 Oct;184(19):5261-74. doi: 10.1128/JB.184.19.5261-5274.2002.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Betaproteobacteria / growth & development
  • Betaproteobacteria / metabolism*
  • Biodegradation, Environmental
  • Catechols / chemistry*
  • Catechols / metabolism*
  • Intramolecular Lyases / metabolism
  • Lactones / chemistry
  • Lactones / metabolism
  • Magnetic Resonance Spectroscopy
  • Sorbic Acid / analogs & derivatives*
  • Sorbic Acid / chemistry
  • Sorbic Acid / metabolism
  • Toluene / analogs & derivatives*
  • Toluene / chemistry
  • Toluene / metabolism*


  • Catechols
  • Lactones
  • Toluene
  • muconic acid
  • 2,4-dichlorotoluene
  • muconolactone
  • Intramolecular Lyases
  • chloromuconate cycloisomerase
  • Sorbic Acid