Sensory perception in bacterial cyclic diguanylate signal transduction

Cyclic diguanylate (c-di-GMP) signal transduction systems provide bacteria the ability to sense changing cell status or environmental conditions and then execute suitable physiological and social behaviours in response. In this review, we provide a comprehensive census of the stimuli and receptors that are linked to modulation of intracellular c-di-GMP. Emerging evidence indicates that c-di-GMP networks sense light, surfaces, energy, redox potential, respiratory electron acceptors, temperature, and structurally diverse biotic and abiotic chemicals. Bioinformatic analysis of sensory domains in diguanylate cyclases and c-di-GMP-specific phosphodiesterases as well as the receptor complexes associated with them reveals that these functions are linked to a diverse repertoire of protein domain families. We describe the principles of stimulus perception learned from studying these modular sensory devices, illustrate how they are assembled in varied combinations with output domains, and summarize a system for classifying these sensor proteins based on their complexity. Biological information-processing via c-di-GMP signal transduction is not only fundamental to bacterial survival in dynamic environments, but also is being used to engineer gene expression circuitry and synthetic proteins with à la carte biochemical functionalities.