Abstract
Actinobacillus actinomycetemcomitans is a periodontopathogenic bacterium associated with active lesions of localized aggressive periodontitis. Cells of A. actinomycetemcomitans grown to mid-log phase, diluted or undiluted, and subjected to a sublethal heat stress demonstrated a partial protection to a subsequent lethal heat stress. On the contrary, stationary phase heat-stressed cells did not exhibit this transient thermal protection. Heat-stressed cells at sublethal temperature showed a higher expression of GroEL and DnaK proteins by immunoblotting, which was in agreement with de novo synthesis. A. actinomycetemcomitans was found to be more sensitive to a pH than to a heat stress. A transient protection to a lethal acid stress was demonstrated when cells were previously subjected to a sublethal acid stress. On the contrary, such transient protection did not occur for alkaline stresses. DnaK but not GroEL proteins made up a high proportion of the total protein synthesized following acid stress. The protection phenomenon is highly complex and heat shock proteins, which may help A. actinomycetemcomitans to support subsequent lethal conditions, are not expressed in the same way during the different stresses investigated.