Characterization of c-di-AMP signaling in the periodontal pathobiont, Treponema denticola.

Pathobionts associated with periodontitis, such as Treponema denticola, must possess numerous sensory transduction systems to adapt to the highly dynamic subgingival environment. To date, the signaling pathways utilized by T. denticola to rapidly sense and respond to environmental stimuli are mainly unknown. Bis-(3'-5') cyclic diadenosine monophosphate (c-di-AMP) is a nucleotide secondary messenger that regulates osmolyte transport, central metabolism, biofilm development, and pathogenicity in many bacteria but is uncharacterized in T. denticola. Here, we studied c-di-AMP signaling in T. denticola to understand how it contributes to T. denticola physiology. We demonstrated that T. denticola produces c-di-AMP and identified enzymes that function in the synthesis (TDE1909) and hydrolysis (TDE0027) of c-di-AMP. To investigate how c-di-AMP may impact T. denticola cellular processes, a screening assay was performed to identify putative c-di-AMP receptor proteins. This approach identified TDE0087, annotated as a potassium uptake protein, as the first T. denticola c-di-AMP binding protein. As potassium homeostasis is critical for maintaining turgor pressure, we demonstrated that T. denticola c-di-AMP concentrations are impacted by osmolarity, suggesting that c-di-AMP negatively regulates potassium uptake in hypoosmotic solutions. Collectively, this study demonstrates T. denticola utilizes c-di-AMP signaling, identifies c-di-AMP metabolism proteins, identifies putative receptor proteins, and correlates c-di-AMP signaling to osmoregulation.