Objective In order to determine the function of PG0839 gene from Porphyromonas gingivalis（P.gingivalis） W83 strains, we intended to create a mutant in the PG0839 gene by homologous recombination. Methods 1 584 bp PG0839 gene fragment was amplified, digested by BamH Ⅰ and EcoR Ⅰ, purified and ligated to pUC19. The recombinant plasmid was designated as pPG0839-1. The erm cassette（2 101 bp） was inserted into the EcoR Ⅴ restriction site of the PG0839 gene. The resultant recombinant plasmid, pPG0839-2, was used as a donor in the electroporation of P.gingivalis W83. After electroporated and selected on erythromycin brain heart infusion plates, a single colony was collected and designated as PG0839 gene-defective mutant. Results A mutant in PG0839 gene was created by insertional inactivation, and inactivation of PG0839 gene was confirmed by restriction endonuclease digestive, sequencing, polymerase chain reaction（PCR） and reverse transcription PCR. Conclusion A PG0839 gene-defective mutant was created successfully.
