The hybrid sensor kinase RscS integrates positive and negative signals to modulate biofilm formation in Vibrio fischeri

Department of Microbiology and Immunology, Loyola University Chicago, Maywood, IL 60153

^* To whom correspondence should be addressed. Email: kvisick{at}lumc.edu.

	Abstract

Overexpression of the Vibrio fischeri sensor kinase RscS induces expression of the symbiosis polysaccharide (syp) gene cluster and promotes biofilm phenotypes such as wrinkled colony morphology, pellicle formation and surface adherence. RscS is predicted to be a hybrid sensor kinase with a histidine kinase/ATPase domain (HATPase), a receiver-like domain (Rec) and a histidine phosphotransferase domain (Hpt). Bioinformatic analysis also revealed three potential signal detection domains within RscS: two transmembrane helices forming a transmembrane region (TMR), a large periplasmic (PP) domain and a cytoplasmic PAS domain. In this work, we genetically dissected the contribution of these domains to RscS function. Substitutions within the carboxy-terminal domain supported the identification of RscS as a hybrid sensor kinase: disruption of both HATPase and Rec domains abolished induction of syp transcription, wrinkled colony morphology, pellicle formation and surface adherence, while disruption of Hpt resulted in decreased activity. The PAS domain was also critical for RscS activity; substitutions in PAS resulted in a loss of activity. Generation of a cytoplasmic, N-terminal deletion derivative of RscS resulted in partial loss of activity, suggesting a role for localization to the membrane and/or sequences within the TMR and PP domain. Finally, substitutions within the first transmembrane helix of the TMR and deletions within the PP domain both resulted in increased activity. Thus, RscS integrates both inhibitory and stimulatory signals from the environment to regulate biofilm formation by V. fischeri.