The recA gene in Porphyromonas gingivalis is expressed during infection ofthe murine host

The recA gene in Porphyromonas gingivalis is involved in DNA repair. To fur ther elucidate the importance of the recA locus in the pathogenesis of P. g ingivalis, we assessed its ability for expression in an animal host. The pr omoterless xa-tet(Q)2 cassette was used in heterodiploid mutants to study r ecA promoter activity during infection. P. gingivalis FLL118.1 had the xa-t etA(Q)2 cassette under the control of recA promoter whereas P. gingivalis F LL119 had the cassette in the opposite orientation. xa encodes a bifunction al xylosidase/arabinosidase enzyme (XA) and the tetA(Q)2 gene product confe rs tetracycline resistance. Intramuscular infection in a mouse model allowe d the recovery of the bacteria from inguinal lymph nodes. Infusion of tetra cycline in the animals permitted the enrichment P. gingivalis FLL118.1 over the wild-type strain, during a mixed infection. The xylosidase activity of FLL118.1 could be detected on agar plates in the presence of 5-methylumbel lifiry-beta -D-xyloside. No such enrichment for xylosidase activity was det ected when the mixture of P. gingivalis W83 and P. gingivalis FLL119 was us ed to infect the mouse or cultured in vitro. These results indicated that r ecA promoter was transcriptionally active during the infection of the murin e host and further support the importance of this locus during the P. gingi valis infection process.