A Bacteriophytochrome Mediates Interplay between Light Sensing and the Second Messenger Cyclic Di-GMP to Control Social Behavior and Virulence.

Bacteriophytochromes are the most abundant and ubiquitous light-sensing receptors in bacteria and are involved in time-of-day behavior or responses. However, their biological and regulatory role in non-photosynthetic bacteria is poorly understood, and even less is known about how they regulate diverse cellular processes. Here, we show that a bacteriophytochrome (XooBphP) from the plant pathogen Xanthomonas oryzae pv. oryzae perceives light signals and transduces a signal through its EAL-mediated phosphodiesterase activity, modulating the intracellular level of the ubiquitous bacterial second messenger c-di-GMP. We discover that light-mediated fine-tuning of intracellular c-di-GMP levels by XooBphP regulates production of virulence functions, iron metabolism, and transition from a sessile to a free-swimming motile lifestyle, contributing to its colonization of the host and virulence. XooBphP thus plays a crucial role in integrating photo-sensing with intracellular signaling to control the pathogenic lifestyle and social behavior.