Porphyromonas gingivalis is a key pathogen responsible for initiation and progression of chronic periodontitis. Little is known about the regulatory mechanisms of iron and heme uptake that allow P. gingivalis to express virulence factors and survive in the hostile environment of the oral cavity, so we initiated characterization of a P. gingivalis Fur homolog (PgFur). Many Fur paralogs found in microbial genomes, including Bacteroidetes, confirm that Fur proteins have a tendency to be subjected to a sub- or even neofunctionalization process. PgFur revealed extremely high sequence divergence, which could be associated with its functional dissimilarity in comparison with other Fur homologs. A fur mutant strain constructed by insertional inactivation exhibited retarded growth during the early growth phase and a significantly lower tendency to form a homotypic biofilm on abiotic surfaces. The mutant also showed significantly weaker adherence and invasion to epithelial cells and macrophages. Transcripts of many differentially regulated genes identified in the fur mutant strain were annotated as hypothetical proteins, suggesting that PgFur can play a novel role in the regulation of gene expression. Inactivation of the fur gene resulted in decreased hmuY gene expression, increased expression of other hmu components and changes in the expression of genes encoding hemagglutinins and proteases (mainly gingipains), HtrA, some extracytoplasmic sigma factors and two-component systems. Our data suggest that PgFur can influence in vivo growth and virulence, at least in part by affecting iron/heme acquisition, allowing efficient infection through a complex regulatory network.
Porphyromonas gingivalis, a major etiological agent of chronic periodontitis, acquires heme from host hemoproteins using the HmuY hemophore. The aim of this study was to develop a specific P. gingivalis marker based on a hmuY gene sequence. Subgingival samples were collected from 66 patients with chronic periodontitis and 40 healthy subjects and the entire hmuY gene was analyzed in positive samples. Phylogenetic analyses demonstrated that both the amino acid sequence of the HmuY protein and the nucleotide sequence of the hmuY gene are unique among P. gingivalis strains/isolates and show low identity to sequences found in other species (below 50 and 56%, respectively). In agreement with these findings, a set of hmuY gene-based primers and standard/real-time PCR with SYBR Green chemistry allowed us to specifically detect P. gingivalis in patients with chronic periodontitis (77.3%) and healthy subjects (20%), the latter possessing lower number of P. gingivalis cells and total bacterial cells. Isolates from healthy subjects possess the hmuY gene-based nucleotide sequence pattern occurring in W83/W50/A7436 (n = 4), 381/ATCC 33277 (n = 3) or TDC60 (n = 1) strains, whereas those from patients typically have TDC60 (n = 21), W83/W50/A7436 (n = 17) and 381/ATCC 33277 (n = 13) strains. We observed a significant correlation between periodontal index of risk of infectiousness (PIRI) and the presence/absence of P. gingivalis (regardless of the hmuY gene-based sequence pattern of the isolate identified [r = 0.43; P = 0.0002] and considering particular isolate pattern [r = 0.38; P = 0.0012]). In conclusion, we demonstrated that the hmuY gene sequence or its fragments may be used as one of the molecular markers of P. gingivalis.
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