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J. Bacteriol., 05 1995, 2789-2797, Vol 177, No. 10
EA Sia, RC Roberts, C Easter, DR Helinski and DH Figurski
The par region of the broad-host-range, IncP alpha plasmid RK2 has been
implicated as a stability determinant by its ability to enhance the
maintenance of mini-RK2 plasmids or heterologous replicons in a growing
population of host cells. The region consists of two operons: parCBA, which
encodes a multimer resolution system, and parDE, which specifies a
postsegregational response mechanism that is toxic to plasmidless
segregants. To assess the importance of this region to the stable
maintenance of the complete RK2 plasmid in different hosts, we used the
vector-mediated excision (VEX) deletion system to specifically remove the
entire par region or each operon separately from an otherwise intact RK2
plasmid carrying a lacZ marker. The par region was found to be important to
stable maintenance of RK2lac (pRK2526) in Escherichia coli and five other
gram-negative hosts (Agrobacterium tumefaciens, Azotobacter vinelandii,
Acinetobacter calcoaceticus, Caulobacter crescentus, and Pseudomonas
aeruginosa). However, the relative importance of the parCBA and parDE
operons varied from host to host. Deletion of parDE had no effect on the
maintenance of pRK2526 in A. calcoaceticus, but it severely reduced pRK2526
maintenance in A. vinelandii and resulted in significant instability in the
other hosts. Deletion of parCBA did not alter pRK2526 stability in E. coli,
A. tumefaciens, or A. vinelandii but severely reduced plasmid maintenance
in A. calcoaceticus and P. aeruginosa. In the latter two hosts and C.
crescentus, the delta parCBA mutant caused a notable reduction in growth
rate in the absence of selection for the plasmid, indicating that
instability resulting from the absence of parCBA may trigger the
postsegregational response mediated by parDE.(ABSTRACT TRUNCATED AT 250
WORDS)
Copyright © 1995, American Society for Microbiology
Different relative importances of the par operons and the effect of conjugal transfer on the maintenance of intact promiscuous plasmid RK2
Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
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