Behavior of the IncW plasmid Sa in Zymomonas mobilis

The stability of the broad-host-range IncW R plasmid Sa in Zymomonas mobilis ZM6100(Sa) was monitored using three antibiotic resistance markers carried by Sa. When grown in batch culture without selection, ZM6100(Sa) rapidly lost the Sa plasmid. When grown with selection for either kanamycin or spectinomycin resistance, the three Sa markers were retained in at least 90% of the population, with spontaneous loss of chloramphenicol resistance being observed in the rest of the population. When ZM6100(Sa) was grown with selection for chloramphenicol resistance, the Sa plasmid either formed a cointegrate plasmid, designated pNSW301, with a native ZM6100 plasmid or was lost except for the chloramphenicol resistance marker. Possible transportation of the chloramphenicol resistance region of Sa to the Z. mobilis chromosome was indicated by hybridization data. The cointegrate plasmid, pNSW301, was maintained stably, except for spontaneous loss of chloramphenicol resistance, in Z. mobilis without selection for 300 generations. pNSW301 was able to replicate in Escherichia coli and was capable of conjugal transfer.