An ultraviolet-sensitive mutant of Zymomonas mobilis affecting the stability of its natural plasmid pZMO2.

Plasmid pZMO2, a 1.9-kb natural plasmid of Zymomonas mobilis strain ATCC 10988, was found to be absent from the extract of a mutant isolate sensitive to ultraviolet irradiation, methyl methanesulfonic acid, and mitomycin C. This mutant, named uvs51, also exhibited extremely high segregational instability of the recombinant plasmid pDS212, whose maintenance in the parental strain is known to be due to pZMO2 sequences. Helped conjugations, employing uvs51 as recipient with Escherichia coli donors containing the conjugative plasmid pRK2013 and a mobilizable recombinant plasmid carrying the Rhizobium meliloti recA gene, showed complementation of uvs51 with the recA functions. Moreover, uvs51/recA stable transconjugants, containing the recA sequence integrated into their chromosomes, showed an increased stability of recombinant plasmid pDS212. The data presented here indicate that the stable maintenance of the natural plasmid pZMO2 in Z. mobilis is affected by a putative recA function.