Plasmid mediated mineralization of 4-chlorobiphenyl

Strains of Alcaligenes and Acinetobacter spp. were isolated from a mixed culture already proven proficient at complete mineralization of monohalogenated biphenyls. We showed that these strains harbored a 35 x 10⁶ dalton plasmid mediating a complete pathway for 4-chlorobiphenyl (4CB) oxidation. Subsequent plasmid curing of these bacteria resulted in the abolishment of all 4CB mineralization phenotype and loss of even early 4CB metabolism by the Acinetobacter spp. Reestablishment of the Alcaligenes plasmid, denoted pSS, in the cured Acinetobacter spp., via filter surface mating, resulted in the restoration of 4CB mineralization abilities. 4CB mineralization, however, proved to be an unstable character in some strains, easily lost on subculture. Such loss was not found to coincide with any detectable alteration in plasmid size. Cultures capable of complete mineralization, as well as those limited to partial metabolism of 4CB, produced 4-chlorobenzoate as a metabolite. Demonstration of mineralization of a purified ¹⁴C-labeled chlorobenzoate showed it to be a true intermediate in 4CB mineralization. Unlike the mineralization capability, the ability to produce chlorobenzoate has proven stable on subculture. These results indicate the occurrence of a novel plasmid, or evolved catabolic plasmid, mediating the complete mineralization of 4-chlorobiphenyl.