Ten bacterial strains encoding degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) were isolated from soil by enrichment with this compound. Six of these isolates harboured plasmids encoding degradation of 2,4-D and the related herbicide
2-methyl-4-chlorophenoxyacetic acid (MCPA).
Four plasmids, pJP3,pJP4, pJP5 and pJP7 had molecular weights of 51 Mdal, belonged to the P-1 incompatibility group and transferred to strains of Escherichia coli, Rhodopseudomonas sphaeroides, Rhizobium sp., Agrobacterium tumefaciens, Pseudomonas putida, Pseudomonas flourescens and Acinetobacter calcoaceticus. In addition, these four plasmids conferred resistance to merbromin, phenylmercuric acetate and mercuric chloride, had almost identical EcoRl restriction endonuclease
cleavage patterns and encoded degradation of 3-chlorobenzoate.
The remaining two plasmids, pJP2 and pJP9 belonged to the Cd incompatibility group, had molecular weights of 37 Mdal, encoded degradation of phenoxyacetic acid and possessed identical EcoR1 restriction endonuclease cleavage patterns. These plasmids transferred to Escherichia coli, Agrobacterium tumefaciens and Pseudomonas flourescens.
A map of the EcoR1, BamH1 and Hind111 restriction endonuclease cleavage sites on one plasmid, pJP4, was determined by physical analysis of cloned Hind111 fragments, transposon Tn5 and Tn1771 insertion mutants and transposon Tn1771 generated deletion mutants. Genetic analysis of these mutants enabled localization of genes encoding degradation of 2,4-D and 3-chlorobenzoate, resistance to mercuric
chloride and merbromin and plasmid maintenance and transfer functions. Transposon mutagenesis of genes encoding 2,4-D and 3-chlorobenzoate degradation indicated that these genes were linked on pJP4.