5-Chloropicolinic acid is produced by specific degradation of 4-chlorobenzoic 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 degrada tion products and determine the degradation pathways to ensure that compoun ds more toxic or mobile than the original contaminants are not produced, In the degradation of 4-chlorobiphenyl, S. paucimobilis BPSI-3 produces a nov el chlorinated picolinic acid, In this paper, we show that 4-chlorobenzoate is an intermediate in this degradation and, through N-15-labelling, that 5 -chloropicolinate is the only nitrogenous metabolite isolated under the ext raction conditions used, The position of the chlorine indicates that degrad ation of 4-chlorocatechol occurs exclusively via a 2,3-extradiol cleavage, These data allow us to postulate a more definitive catabolic pathway for th e biodegradation of 4-chlorobiphenyl to 5-chloro-2-hydroxymuconic acid semi aldehyde via 4-chlorobenzoate in S. paucimobilis BPSI-3.