Microbial metabolism of polychlorinated biphenyls. Studies on the relative degradability of polychlorinated biphenyl components by Alkaligenes sp
Furukawa, K.; Matsumura, F.
Journal of Agricultural and Food Chemistry 24(2): 251-256
ISSN/ISBN: 0021-8561 PMID: 815303 DOI: 10.1021/jf60204a002
A bacterial strain belonging to the genus Alcaligenes was isolated from a lake sediment by using biphenyl as a sole C source. Metabolic degradation of various polychlorinated biphenyls (PCB) by this organism was studied. The bacterium was capable of metabolizing various PCB components, including a highly chlorinated one such as 2,4,5,2',5'-pentachlorobiphenyl, through an oxidative route. The organism appears to preferentially degrade the less chlorinated (ring II) of the 2 rings. Degradation takes place in 2 major steps. The 1st step produces metabolic intermediates which are considered to be chlorinated derivatives of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid, which often has a yellow color with an absorption around 400 nm. In the 2nd step these colored metabolic intermediates are degraded to corresponding chlorobenzoic acids. Among the colored intermediates, the ones derived from PCB components with a chlorine substitution at the 4' position on ring II particularly exhibited a long lasting yellow color indicating the stability of the intermediates. Among chlorinated benzoic acids, meta chloro substitutes derived from PCB components with a 3- or 3'-Cl substitution appeared to be further metabolized by this organism. PCB components with all the Cl's only on one ring degraded relatively fast as compared to those possessing an equivalent number of Cl's on both rings. Generally, degradation of PCBs becomes increasingly difficult as the degree of chlorination increases.