Narrow-host-range IncP Plasmid pHH502-1 Lacks a Complete IncP Replication System

SUMMARY: Plasmid pHH502-1 shows incompatibility only towards members of the IncP group, but has a narrower host range than typical members of that group. In contrast to other IncP plasmids its replication was not affected by a high-copy-number plasmid carrying the replication origin (oriV) of IncP plasmid RK2. Southern blotting of pHH502-1 revealed homology to oriV, consistent with its incompatibility phenotype, but no homology to trfA, the essential replication gene of RK2. Thus it is probable that pHH502-1 does not possess a functional IncP replication system, accounting for its restricted host range. A restriction map of pHH502-1 was constructed and the mercury-resistance determinant was localized to Tn735, which also carries the trimethoprim-resistance determinant and is related to Tn21. The presence of a korB-like function on pHH502-1 was also demonstrated.