Red Light Activates the σ B - Mediated General Stress Response of Bacillus subtilis via the Energy Branch of the Upstream Signaling Cascade

Abstract

ABSTRACT The σ B -dependent general stress response in the common soil bacterium Bacillus subtilis can be elicited by a range of stress factors, such as starvation or an ethanol, salt, or heat shock, via a complex upstream signaling cascade. Additionally, σ B can be activated by blue light via the phototropin homologue YtvA, a component of the environmental branch of the signaling cascade. Here we use a reporter-gene fusion to show that σ B can also be activated by red light via the energy branch of its upstream signaling cascade. Deletion mutagenesis and homologous overproduction experiments indicate that the RsbP protein (composed of an N-terminal Per-ARNT-Sim [PAS] domain and a C-terminal PP2C-type phosphatase domain) is involved in the red light response. This second light input pathway functions complementarily to YtvA; it shows broader spectral sensitivity but requires higher light intensities. These results are confirmed by transcriptome analyses, which show that both light effects result in upregulation of the σ B regulon, with minimal activation of other responses.