Activation of the General Stress Response of Bacillus subtilis by Visible Light

A key challenge for microbiology is to understand how evolution has shaped the wiring of regulatory networks. This is amplified by the paucity of information of power-spectra of physicochemical stimuli to which microorganisms are exposed. Future studies of genome evolution, driven by altered stimulus regimes, will therefore require a versatile signal transduction system that allows accurate signal dosing. Here, we review the general stress response of Bacillus subtilis, and its upstream signal transduction network, as a candidate system. It can be activated by red and blue light, and by many additional stimuli. Signal integration therefore is an intricate function of this system. The blue-light response is elicited via the photoreceptor YtvA, which forms an integral part of stressosomes, to activate expression of the stress regulon of B. subtilis. Signal transfer through this network can be assayed with reporter enzymes, while intermediate steps can be studied with live-cell imaging of fluorescently tagged proteins. Different parts of this system have been studied in vitro, such that its computational modeling has made significant progress. One can directly relate the microscopic characteristics of YtvA with activation of the general stress regulon, making this system a very well-suited system for network evolution studies.