Nucleotide sequence of the Porphyromonas gingivalis W83 recA homolog and construction of a recA-deficient mutant

Degenerate oligonucleotide primers were used in PCR to amplify a region of the recA homolog from Porphyromonas gingivalis W83. The resulting PCR fragment was used as a probe to identify a recombinant h DASH phage (L10) carrying the P. gingivalis recA homolog. The read homolog was localized to a 2.1-kb BamHI fragment. The nucleotide sequence of this 2.1-kb fragment was determined, and a 1.02-kb open reading frame (341 amino acids) was detected. The predicted amino acid sequence was strikingly similar (90% identical residues) to the RecA protein from Bacteroides fragilis. No SOS box, characteristic of LexA-regulated promoters, was found in the 5' upstream region of the P. gingivalis read homolog. In both methyl methanesulfonate and UV survival experiments the read homolog from P. gingivalis complemented the recA mutation of Escherichia coli HB101. The cloned P. gingivalis recA gene was insertionally inactivated with the ermF-ermA antibiotic resistance cassette to create a recA-deficient mutant (FLL33) by allelic exchange. The recA-deficient mutant was significantly more sensitive to LW irradiation than the wild-type strain, W83, W83 and FLL33 showed the same level of virulence in in vivo experiments using a mouse model. These results suggest that the recA gene in P. gingivalis W83 plays the expected role of repairing DNA damage caused by UV irradiation. However, inactivation of this gene did not alter the virulence of P. gingivalis in the mouse model.