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Environmental regulation of fimbrial gene expression in Porphyromonas gingivalis
H Xie1, S Cai, R J Lamont
1Department of Oral Biology, University of Washington, Seattle 98195-7132, USA.
Abstract:
Porphyromonas gingivalis fimbriae are an important virulence factor involved in attachment and invasion. Fimbrillin, encoded by the fimA gene, is the major subunit protein of the fimbriae. To elucidate the influence of environmental signals on the expression of the fimA gene, a strain of P. gingivalis (designated PLE) containing a chromosomal transcriptional fusion between a promoterless lacZ gene and the fimA promoter region was constructed. Promoter activity was assessed by measurement of beta-galactosidase activity of PLE. An 11-fold increase in activity of fimA promoter was found as growth temperature declined from 39 to 34 degrees C. Promoter activity decreased by approximately 50% in response to hemin limitation and upon culture on solid medium. In addition, the presence of serum or saliva in the growth medium decreased fimA promoter activity by similar amounts. A correlation between fimA promoter activity and phenotypic properties dependent upon fimbriae was established. P. gingivalis grown at 34 degrees C, compared to 39 degrees C, showed an increased ability to adhere to Streptococcus gordonii and to invade primary cultures of gingival epithelial cells. These studies indicate that expression of the P. gingivalis fimA gene is regulated at the transcriptional level in response to several environmental conditions and that altered fimA expression can also modulate the adherence and invasion abilities of P. gingivalis.
Insights
Environmental signals like temperature and nutrient availability regulate Porphyromonas gingivalis fimA gene expression. This regulation impacts the bacteria's ability to adhere to and invade host cells, crucial for virulence.
Area of Science:
- Microbiology
- Molecular Biology
- Oral Health
Background:
- Porphyromonas gingivalis fimbriae are key virulence factors.
- Fimbrillin, the main subunit of fimbriae, is encoded by the fimA gene.
- Understanding fimA gene regulation is vital for P. gingivalis virulence research.
Purpose of the Study:
- To investigate how environmental signals influence fimA gene expression in P. gingivalis.
- To correlate fimA gene expression levels with P. gingivalis adherence and invasion capabilities.
Main Methods:
- Constructed a P. gingivalis strain (PLE) with a fimA promoter-lacZ transcriptional fusion.
- Measured beta-galactosidase activity to assess fimA promoter activity under various conditions.
- Evaluated bacterial adherence to Streptococcus gordonii and invasion of gingival epithelial cells.
Main Results:
- fimA promoter activity increased 11-fold as temperature decreased from 39°C to 34°C.
- Hemin limitation, solid medium, serum, and saliva reduced fimA promoter activity by approximately 50%.
- Lower temperature (34°C) correlated with increased adherence and invasion capabilities.
Conclusions:
- P. gingivalis fimA gene expression is transcriptionally regulated by environmental factors.
- Environmental modulation of fimA expression directly affects P. gingivalis adherence and invasion.
- Findings provide insights into P. gingivalis pathogenesis and virulence mechanisms.