Environmental regulation of recA gene expression in Porphyromonas gingivalis

The recA gene product in Porphyromonas gingivalis is involved in DNA repair . Further, disruption of this gene can affect the proteolytic activity and expression of other virulence factors in this organism. Since several known environmental factors can influence virulence gene expression in P. gingiv alis, we investigated the influence of these signals on the expression of t he recA gene in this organism. A heterodiploid strain of P. gingivalis (des ignated FLL 118) containing a transcriptional fusion of the recA promoter r egion and the promoterless tetracycline-resistant gene [tetA (Q)2] and xylo sidase/arabinosidase (xa) gene cassette was constructed. The recA promoter activity was assessed by measurement of xylosidase activity in FLL118. The expression remained relatively constant during different growth phases, at different pH levels and in the presence of DNA-damaging agents. In response to hemin limitation and in the presence of calcium there was a moderate in crease in recA promoter activity. Temperature also affected the expression. The highest level of xylosidase activity was observed in cultures at 32 de greesC with a decline of approximately 46% as growth temperature increased to 41 degreesC. Reverse transcriptase polymerase chain reaction analysis re vealed that this regulation may be occurring at the transcriptional level. These results suggest that expression of the recA gene in P. gingivalis W83 is responsive to several environmental signals but is not regulated by a D NA damage-inducible SOS-like regulatory system.