Transformation of chlorinated benzenes and toluenes by Ralstonia sp strainPS12 tecA (tetrachlorobenzene dioxygenase) and tecB (chlorobenzene dihydrodiol dehydrogenase) gene products

The tecB gene, located downstream of tecA and encoding tetrachlorobenzene d ioxygenase, in Ralstonia sp. strain PS12 was cloned into Escherichia coli D H5 alpha together with the tecA gene. The identity of the tecB gene product as a chlorobenzene dihydrodiol dehydrogenase was verified by transformatio n into the respective catechols of chlorobenzene, the three isomeric dichlo robenzenes, as well as 1,2,3- and 1,2,4-trichlorobenzenes, all of which are transformed by TecA into the respective dihydrodihydroxy derivatives. Di- and trichlorotoluenes were either subject to TecA-mediated dioxygenation (t he major or sole reaction observed for the 1,2,4-substituted 2,4-, 2,5-, an d 3,4-dichlorotoluenes), resulting in the formation of the dihydrodihydroxy derivatives, or to monooxygenation of the methyl substituent (the major or sole reaction observed for 2,3-, 2,6-, and 3,5-dichloro- and 2,4,5-trichlo rotoluenes), resulting in formation of the respective benzyl alcohols. All of the chlorotoluenes subject to dioxygenation by TecA were transformed, wi thout intermediate accumulation of dihydrodihydroxy derivatives, into the r espective catechols by TecAB, indicating that dehydrogenation is no bottlen eck for chlorobenzene or chlorotoluene degradation. However, only those chl orotoluenes subject to a predominant dioxygenation were growth substrates f or PS12, confirming that monooxygenation is an unproductive pathway in PS12 .