Detection and characterization of plasmids in chloridazon and antipyrin degrading bacteria

Abstract

All of 19 different strains of soil bacteria with the ability to utilize chloridazon (5-amino-4-chloro-2-phenyl-3-(2H)-pyridazinone) and antipyrin (2,3-dimethyl-1-phenyl-pyrazolone) as the only carbon source have been shown to harbour plasmid DNA. By agarose gel electrophoresis the presence of at least two different plasmids was demonstrated for all strains, several strains were shown to contain three, four or even six plasmids. Regarding the size of the plasmids considerable variations within the different plasmids of one strain and among the different bacterial strains have been observed. Molecular weights in the range of 8.0 to 300 Md were found.

Evidence is presented for a correlation of degradative capacity and the presence of plasmids: Strains K2 and K3 which are able to utilize antipyrin as their sole carbon source, were found to loose this capacity spontaneously by repeated transfers on antipyrin-free media, giving rise to mutant strains with the phenotypes Phe⁺AP⁻. These mutants were found to be devoid of the first enzyme of the degradation of antipyrin (dioxygenase). No revertants to the wild types were obtained hitherto. Both mutant strains were found to contain only one plasmid of 14.0 Md. The wild types (Phe⁺AP⁺), however, contain two plasmids of 21.5, 14.0 Md (K2) and of 20.2, 14.0 Md (K3). The 14.0 Md plasmid was shown to be identical in strains K2 and K3 (Phe⁺AP⁺ and Phe⁺AP⁻) by restriction endonuclease cleavage and by hybridization experiments. The existence of two pathways for the metabolism of phenylalanine, one assumed to be plasmidborne the other one encoded by chromosomal genes, is discussed.