5-Chloropicolinic acid is produced by specific degradation of 4chlorobenzoic acid by Sphingomonas paucimobilis BPSI-3

We have previously shown that the bacterium Sphingomonas paucimobilis BPSI-3, isolated from PCB-contaminated soil, can degrade halogenated biphenyls, naphthalenes, catechols and benzoic acids. However, before such an organism can be used in bioremediation, it is important to characterise the degradation products and determine the degradation pathways to ensure that compounds more toxic or mobile than the original contaminants are not produced. In the degradation of 4-chlorobiphenyl, S. paucimobilis BPSI-3 produces a novel chlorinated picolinic acid. In this paper, we show that 4- chlorobenzoate is an intermediate in this degradation and, through ¹⁵N- labelling, that 5-chloropicolinate is the only nitrogenous metabolite isolated under the extraction conditions used. The position of the chlorine indicates that degradation of 4-chlorocatechol occurs exclusively via a 2,3- extradiol cleavage. These data allow us to postulate a more definitive catabolic pathway for the biodegradation of 4-chlorobiphenyl to 5-chloro2- hydroxymuconic acid semialdehyde via 4-chlorobenzoate in S. paucimobilis BPSI-3.