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

Publisher Website
Google Scholar
Abstract
The periodontal pathogenPorphyromonas gingivalisemploys a variety of mechanisms for the uptake of hemin and inorganic iron. Previous work demonstrated that hemin uptake inP. gingivalismay be controlled by LuxS-mediated signaling. In the present study, the expression of genes involved in hemin and iron uptake was determined in parent andluxSmutant strains by quantitative real-time reverse transcription-PCR. Compared to the parental strain, theluxSmutant 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 Fe2+ion transport protein, FeoB1; and the iron storage protein ferritin. Differential expression of these genes in theluxSmutant was maximal in early-exponential phase, which corresponded with peak expression ofluxSand AI-2 signal activity. Complementation of theluxSmutation with wild-typeluxSintransrescued expression ofhmuR. Mutation of the GppX two-component signal transduction pathway caused an increase in expression ofluxSalong withtlrand lower levels of message forhmuR. Moreover, expression ofhmuRwas repressed, and expression oftlrstimulated, when theluxSmutant 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 theluxSmutant in hemin-depleted medium. The results demonstrate a role of LuxS/AI-2 in the regulation of hemin and iron acquisition pathways inP. gingivalisand reveal a novel control pathway forluxSexpression.