Regulation of humYR by a transcriptional activator in Porphyromonas gingivalis

OBJECTIVES: One of the features of the periodontal pathogen Porphyromonas gingivalis is its complex iron acquisition systems that include a humYRSTUV locus. The objective is to understand expression and regulation of hum operon.

METHODS: An insertional pg1237 mutant was generated by using ligation-independent cloning of PCR mediated mutagenesis (LIC-PCR). Expression level of hum genes was determined by using real-time PCR.

RESULTS: Here we report that a novel transcriptional activator, PG1237, was required for the expression of humY and humR, but not other iron acquisition-related genes fetB and tlr encoding hemin binding proteins. By using real-time PCR analysis, we show here that expression level of humY and humR in the pg1237 mutant were decreased 90 or 70 fold, respectively, compared to those in the wild type strain. Differential expression of humY, humR and pg1237 were found to be quorum sensing dependent. The higher expression level of these genes was observed when P. gingivalis was grown in lower cell density, such as during the early-exponential-growth phase. Moreover, unlike the previous reports, expression level of humY and humR were not up-regulated in P. gingivalis grown under the hemin limited conditions compared to the organism grown in the presence of hemin but in the similar cell density.

CONCLUSIONS: This work demonstrates an involvement of a novel transcriptional activator in expression of hum operon and a correlation between cell density and expression level of hum operon. Further study of this correlation may lead to discovery of new quorum sensing molecules. This work is supported by Public Health Service grants DE014699 to Hua Xie from the National Institute of Dental and Craniofacial Research.