Ubiquity of plasmids in coding for toluene and xylene metabolism in soil bacteria: evidence for the existence of new TOL plasmids

Abstract

Bacteria (13) were isolated from 9 different soil samples by selective enrichment culture on m-toluate (m-methylbenzoate) minimal medium. Of these were classified as Pseudomonas putida, 1 as a fluorescent Pseudomonas sp. and 4 as nonfluorescent Pseudomonas sp. All 13 strains appeared to carry TOL plasmids superfically similar to that previously described P. putida mt-2 in that: all the wild-type strains could utilize toluene, m-xylene and p-xylene as sole C and energy sources; these growth substrates were metabolized through the corresponding alcohols and aldehydes to benzoate, m-toluate and p-tolutate, respectively, and thence by the divergent meta (or .alpha.-ketoacid) pathway; and the isolates could simultaneously and spontaneously lose their ability to utilize the hydrocarbons, alcohols, aldehydes and acids, particularly during growth on benzoate, giving rise to cured strains which could grow only on benzaldehyde and benzoate, giving rise to cured strains which could grow only on benzaldehyde and benzoate of the aromatic substrates by the alternative ortho (or .beta.-ketoadipate) pathway. Of the isolates were able to transfer their TOL plasmids into their own cured strains, but only 5 were able to transfer them in interstrain conjugation into the cured derivative of P. putida mt-2. P. putida mt-2 could transfer its TOL plasmid into 11 of the cured isolates, and 8 of these were able to retransmit this foreign plasmid in intrastrain conjugation with their own cured derivatives. Of the isolates, MT 14, MT 15 and MT 20 differed significantly from the others in that the wild-type strains dissimilated the p methyl-substitute substrates poorly. During growth on benzoate, in addition to the cured derivatives, they gave rise to derivatives with a phenotype intermediate between the cured and wild-type strains, the biochemical and genetic nature of which was not elucidated.