The Hpk2-Rrp2 two-component regulatory system of Treponema denticola: a potential regulator of environmental and adaptive responses.

Treponema denticola levels in the gingival crevice become elevated as periodontal disease develops. Oral treponemes may account for as much as 40% of the total bacterial population in the periodontal pocket. The stimuli that trigger enhanced growth of T. denticola, and the mechanisms associated with the transmission of these signals, remain to be defined. We hypothesize that the T. denticola open reading frames tde1970 (histidine kinase) and tde1969 (response regulator) constitute a functional two-component regulatory system that regulates, at least in part, responses to the changing environmental conditions associated with the development of periodontal disease. The results presented demonstrate that tde1970 and tde1969 are conserved, universal among T. denticola isolates and transcribed as part of a seven-gene operon in a growth-phase-dependent manner. tde1970 undergoes autophosphorylation and transfers phosphate to tde1969. Henceforth, the proteins encoded by these open reading frames are designated as Hpk2 and Rrp2 respectively. Hpk2 autophosphorylation kinetics were influenced by environmental conditions and by the presence or absence of a PAS domain. It can be concluded that Hpk2 and Rrp2 constitute a functional two-component system that contributes to environmental sensing.