Biophysical and genetic properties of six independently isolated plasmids encoding the degradation of the herbicides 2,4-dichlorophenoxyacetic acid and 4chloro-2-methylphenoxyacetic acid are described. Four of the plasmids, pJP3, pJP4, pJP5, and pJP7, had molecular masses of 51 megadaltons, belonged to the IncPl incompatibility group, and transferred freely to strains of Escherichia coli, Rhodopseudomonas sphaeroides, Rhizobium sp., Agrobacterium tumefaciens, Pseudomonas putida, Pseudomonas fluorescens, and Acinetobacter calcoaceticus. In addition, these four plasmids conferred resistance to merbromin, phenylmercury acetate, and mercuric ions, had almost identical restriction endonuclease cleavage patterns, and encoded degradation of m-chlorobenzoate. The two other plasmids, pJP2 and pJP9, did not belong to the IncPl incompatibility group, had molecular masses of 37 megadaltons, encoded the degradation of phenoxyacetic acid, and possessed identical restriction endonuclease cleavage patterns. Modem agriculture and industry depend on a wide variety of synthetically produced chemicals, including insccides, fungicides, herbicides, and other pesticides. Continual widespread use and release of such synthetics has become an everyday occurrence, resulting in environmental pollution. Although complex in nature, many pesticides, such as the herbicide 2,4dichlorophenoxyacetic acid (2,4-D), are readily degraded by microorganisns present in soil and water (21, 22). In contrast, another closely related herbicide, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), is poorly biodegradable and persists for extended periods in soil (1, 2). Microorganisms capable of 2,4,5-T degradation are
