Abstract
SUMMARY: The sex specific bacteriophage PR4 has been found to plate onP. aeruginosastrains harbouring the TOL catabolic plasmid or the plasmid pND2 derived from TOL. Based on this, attempts were made to place TOL into aPseudomonasplasmid incompatibility group and by showing that pND2 is incompatible with the R plasmid R2, TOL has been placed into the P-9 group. The NAH catabolic plasmid has been reported to be incompatible with TOL, pND2 and a variety of other plasmids derived from TOL. Thus, these plasmids also would appear to belong to the P-9 incompatibility group.