Effect of parB on plasmid stability and gene expression in Xanthomonas campestris

The stabilization locus parB was subcloned into the broad host range plasmid pAP2, which contains the alpha-amylase gene from Bacillus subtilis, and introduced into Xanthomonas campestris pv campestris and X.c.pv manihotis. Analysis of the stability of plasmid pAP2 (parB-) and pAP23 (parB+) showed that the parB locus decreased significantly the plasmid loss rate mainly by X.c.pv campestris. The lower efficiency of stabilization in X.c.pv manihotis was probably due to the incompatibility system between the native plasmids and the newly introduced pAP23. Although parB had conferred higher stability, it determined a lower rate of alpha-amylase activity even by the strain Cm where its stabilization rate was higher.