Further properties of P-2 R-factors of Pseudomonas aeruginosa and their relationship to other plasmid groups.

R-factors of the P-2(prototype R-factor R931) incompatibility group of plasmidsdetected in Pseudomonas are compatible with group P,C,W, and NR-factors which areplasmids that can be transferred to Pseudomonas aeruginosa recipients. Members of the P-2 group (R130,R931) have significant homology by DNA-DNA hybridization. R-factors of the P-group (RP1, RP9) and F-group (R1) exhibited homology with P-2 R-factors but to a lesser extent than R130 with R931. Members of the I, C, and W groups showed no significant homology with P-2 R-factors. Minicircular DNA of strain 931(R931) was not homologous with R931 DNA. The host range of R931 and R130 is limited mainly to certain Pseudomonas species including P. aeruginosa, P. fluorescens, P. putida, and P. stutzeri. These R-factors could not be transferredat detectable frequencies to any member of the Enterobacteriaceae examined. R-factor-specified pili were strongly suggested by the detection of pili by electron microscopyin R-+ but not R- non-piliated mutants of P. aeruginosa strain PA01. The combinedproperties of R-factors 931 and similar R-factors reported before and in this study strongly support our previous contention that this group of R-factors form a significant new group of plasmids. A classification scheme previously proposed for plasmids occurring in Pseudomonas has been modified and four groups have been specified.