FIG. 1.

Construction of site-specific mutanttions by allelic exchange. pFLL91 contains the vimA gene interrupted by an ermF-ermAM cassette. The vimA gene and flanking sequences were amplified by PCR; the ermF-ermAM cassette was purified from pVA2298 (15). The circular recombinant plasmid pFLL91 was integrally introduced into P. gingivalis W83 by electroporation. A reciprocal recombination event between areas of homology on the chromosome and regions flanking the ermAM-ermF cassette on pFLL91 replaced the intact vimA with an inactivated copy.