LuxS Involvement in the Regulation of Genes Coding for Hemin and Iron Acquisition Systems in Porphyromonas gingivalis

Abstract

ABSTRACT The periodontal pathogen Porphyromonas gingivalis employs a variety of mechanisms for the uptake of hemin and inorganic iron. Previous work demonstrated that hemin uptake in P. gingivalis may be controlled by LuxS-mediated signaling. In the present study, the expression of genes involved in hemin and iron uptake was determined in parent and luxS mutant strains by quantitative real-time reverse transcription-PCR. Compared to the parental strain, the luxS mutant showed reduced levels of transcription of genes coding for the TonB-linked hemin binding protein Tlr and the lysine-specific protease Kgp, which can degrade host heme-containing proteins. In contrast, there was up-regulation of the genes for another TonB-linked hemin binding protein, HmuR; a hemin binding lipoprotein, FetB; a Fe 2+ ion transport protein, FeoB1; and the iron storage protein ferritin. Differential expression of these genes in the luxS mutant was maximal in early-exponential phase, which corresponded with peak expression of luxS and AI-2 signal activity. Complementation of the luxS mutation with wild-type luxS in trans rescued expression of hmuR . Mutation of the GppX two-component signal transduction pathway caused an increase in expression of luxS along with tlr and lower levels of message for hmuR . Moreover, expression of hmuR was repressed, and expression of tlr stimulated, when the luxS mutant was incubated with AI-2 partially purified from the culture supernatant of wild-type cells. A phenotypic outcome of the altered expression of genes involved in hemin uptake was impairment of growth of the luxS mutant in hemin-depleted medium. The results demonstrate a role of LuxS/AI-2 in the regulation of hemin and iron acquisition pathways in P. gingivalis and reveal a novel control pathway for luxS expression.