The relationship of degradative and resistance plasmids of Pseudomonas belonging to the same incompatibility group.

Abstract

THE fluorescent pseudomonads include Pseudomonas which can cause serious infections in man, and soil bacteria such as P. putida. Resistance (R) plasmids have been found in strains of both species and degradative (D) plasmids have been demonstrated in strains of the latter species. Where such plasmids can be transferred by conjugation to a common host strain, it has been possible to establish whether they can stably co-exist. Inability to co-exist (incompatibility) is the basis of their classification1,2. It has recently been suggested that both the IncP-2 and IncP-9 groups contain both R and D plasmids2,3. In addition the IncP-2-plasmids are both very large4. Among R plasmids of enterobacteria, incompatibility is generally an indication of evolutionary relationship in that the DNAs of incompatible plasmids show greater homology with each other than with those of compatible plasmids5. However, cases of incompatible plasmids lacking significant homology have also been reported5,6. We have examined the extent to which two R plasmids from P. aeruginosa and two D plasmids, one from P. putida and the other from P. aeruginosa (all assigned to the IncP-9 group3,15,16) share common sequences. The results suggest that plasmids of the same incompatibility group are not necessarily closely related.