Differential display analysis of Porphyromonas gingivalis gene activation response to heat and oxidative stress

The etiologic relationship between periodontitis and Porphyromonas gingivalis is attributed to the ability of the organism to express a variety of virulence factors, many of which are cell surface components including lipopolysaccharide and arginine-specific cysteine proteases (Arg-gingipains, RgpA, and RgpB). P. gingivalis responds to the stress of rapid elevation in temperature by activating a set of genes to produce heat shock proteins that mediate the effects of sudden changes in environmental temperatures by repairing or eliminating cellular proteins denatured by that stress.

We used restriction fragment differential display (RFDD) to identify and measure the genes expressed by surrogates of environmental stresses, heat and oxidative stress. The results were then confirmed using quantitative reverse-transcription polymerase chain reaction.

We selected 16 genes differentially induced from over 800 total expression fragments on the RFDD gels for further characterization. With primers designed from those fragments we found that a + 5 degrees C heat shock caused a statistically significant increase in expression compared 12 of 18 untreated genes tested. The exposure of P. gingivalis to atmospheric oxygen resulted in statistically significant increases in five of the target genes. These genes are likely involved in transport and synthesis of components of the lipopolysaccharide biosynthetic pathway important in anchoring the Arg-gingipains required for virulence-related activities.

These results emphasize the need for studies to measure the coordinated responses of bacteria like P. gingivalis which use a multitude of interrelated metabolic activities to survive the environmental hazards of the infection process.