Co-metabolism of di- and trichlorobenzoates in a 2-chlorobenzoate-degrading bacterial culture : Effect of the position and number of halo-substituents

The degradative properties towards chlorobenzoates by a 2-chlorobenzoate-degrading mixed culture (2MC) were investigated. Although 2MC did not grow on 2,3,5-; 2,3,6- and 2,4,6-trichlorobenzoates, it was able to completely oxidise 2,3,5-trichlorobenzoate and 2,5-dichlorobenzoate. This was degraded through the intermediate formation of 4-chlorocatechol and 3-cis,cis-chloromuconate, suggesting a dioxygenation in 1,2 position. 4-Chlorobenzoate; 3,4- and 2,6-dichlorobenzoate; 2,4,6- and 2,3,6-trichlorobenzoate did not undergo any co-metabolic transformation, the only 2,4-dichlorobenzoate was scarcely transformed into a dichlorinated phenol as end-product. 2MC was constituted of three prominent species: Stenotrophomonas maltophilia, Cupriavidus necator and Flavobacterium sp. Ring-hydroxylating dioxygenase genes (BenA) were retrieved in S. maltophilia and C. necator, indicating the presence of a “modified ortho pathway” in the culture. On the basis of its degradative properties, 2MC could be a good candidate for use in the removal of ortho- and/or meta-chlorobenzoates that are the major end-products of PCB co-metabolism.