Affiliation:
1. Department of Microbiology, University of Stellenbosch, Matieland 7602, South Africa
Abstract
ABSTRACT
Plasmid pTC-F14 contains a plasmid stability system called
pas
(plasmid addiction system), which consists of two proteins, a PasA antitoxin and a PasB toxin. This system is closely related to the
pas
of plasmid pTF-FC2 (81 and 72% amino acid identity for PasA and PasB, respectively) except that the
pas
of pTF-FC2 contains a third protein, PasC. As both pTC-F14 and pTF-FC2 are highly promiscuous broad-host-range plasmids isolated from bacteria that share a similar ecological niche, the plasmids are likely to encounter each other. We investigated the relative efficiencies of the two stability systems and whether they had evolved apart sufficiently for each
pas
to stabilize a plasmid in the presence of the other. The three-component pTF-FC2
pas
was more efficient at stabilization of a heterologous tester plasmid than the two component
pas
of pTC-F14 in
Escherichia coli
host cells (±92% and ±60% after 100 generations, respectively). The PasA antidote of each
pas
was unable to neutralize the PasB toxin of the other plasmid. The
pas
proteins of each plasmid autoregulated their own expression as well as that of the
pas
of the other plasmid. The
pas
of pTF-FC2 was more effective at repressing the
pas
operon of pTC-F14 than the
pas
of pTC-F14 was able to repress itself or the
pas
of pTF-FC2. This increased efficiency was not due to the PasC of pTF-FC2. The effect of this stronger repression was that pTF-FC2 displaced pTC-F14 when the two plasmids were coresident in the same
E. coli
host cell. Plasmid curing resulted in the arrest of cell growth but did not cause cell death, and plasmid stability was not influenced by the
E. coli mazEF
genes.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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