Inheritance of IncP-9 Catabolic Plasmids in Pseudomonas Bacteria

Abstract

This work investigated the capability of the conjugative transfer of epsilon-caprolactam biodegradation (CAP) plasmids, belonging to incompatibility (Inc) groups P-2, P-7, P-9, and IncP-9 naphthalene biodegradation (NAH) plasmids to various species of Pseudomonas bacteria, including strains of plant growth-promoting rhizobacteria (PGPR), and the character of plasmid inheritance in these strains. The frequency of the conjugative transfer of all CAP and NAH plasmids (irrespective of their Inc groups) into Pseudomonas PGPR was shown to be lower than that into P. putida soil strains by more than an order of magnitude. The low frequency of conjugative transfer was found not to be caused by secretion of antibiotically active metabolites by Pseudomonas PGPR strains. Stability of inheritance of catabolic plasmids under nonselective conditions was established to depend on their Inc group and bacterial host strain. Thus, all investigated plasmids were stably maintained in P. putida KT2442 and BS394 strains for at least 100 generations. However, only CAP plasmids of IncP-2 and IncP-7 groups were stably maintained in Pseudomonas PGPR cells. CAP and NAH plasmids of different IncP-9 subgroups were eliminated from cells of rhizosphere pseudomonads within several generations. Thus, the work first revealed inheritance features of IncP-9 catabolic plasmids in Pseudomonas PGPR cells.