Regulon controlled by the GppX hybrid two component system in Porphyromonas gingivalis

The periodontal pathogen Porphyromonas gingivalis experiences a number of environmental conditions in the oral cavity, and must monitor and respond to a variety of environmental cues. However, the organism possesses only five full two‐component systems, one of which is the hybrid system GppX. To investigate the regulon controlled by GppX we performed RNA‐Seq on a ΔGppX mutant. Fifty‐three genes were upregulated and 37 genes were downregulated in the ΔGppX mutant. Pathway analyses revealed no systemic function for GppX under nutrient‐replete conditions; however, over 40% of the differentially abundant genes were annotated as encoding hypothetical proteins indicating a novel role for GppX. Abundance of small RNA was, in general, not affected by the absence of GppX. To further define the role of GppX with respect to regulation of a hypothetical protein observed with the greatest significant relative abundance change relative to a wild‐type control, PGN_0151, we constructed a series of strains in which the ΔgppX mutation was complemented with a GppX protein containing specific domain and phosphotransfer mutations. The transmembrane domains, the DNA‐binding domain and the phosphotransfer residues were all required for regulation of PGN_0151. In addition, binding of GppX to the PGN_0151 promoter regions was confirmed by an electrophoretic mobility shift assay. Both the ΔGppX mutant and a ΔPGN_0151 mutant were deficient in monospecies biofilm formation, suggesting a role for the GppX‐PGN_0151 regulon in colonization and survival of the organism.