Blue light activates the sigmaB-dependent stress response of Bacillus subtilis via YtvA

Abstract

Here we present evidence for a physiologically relevant light response mediated by the LOV domain-containing protein YtvA in the soil bacterium Bacillus subtilis. The loss and overproduction of YtvA abolish and enhance, respectively, the increase in sigma(B)-controlled ctc promoter activity at moderate light intensities. These effects were absent in the dark and in red light but present under blue-light illumination. Thus, activation of the general stress response in B. subtilis is modulated by blue light.

FIG. 1.

Effects of IPTG and light on growth and the σ^B reporter gene P_ctc-lacZ of ytvA-overexpressing and control strains. In all panels, the x axis shows the time after addition of 1 mM IPTG. Cells were incubated in the presence of light (open symbols), in the dark (filled symbols), and in the presence (squares) or absence (triangles) of IPTG. Panels A and C show PB198/pDG148Stu (control). Panels B and D show PB198/pYtvA (ytvA overexpressing). In panels A and B, the y axis shows OD₆₀₀ as a measurement of growth. Panels C and D show β-galactosidase activity (Miller units). Error bars indicate standard deviations calculated from two independent experiments, each with duplicate samples.

FIG. 2.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (20%) of B. subtilis cells producing the YtvA protein (stained with Coomassie brilliant blue). Lane 1, molecular mass standards; lane 2, extracts from strain PB198/pYtvA in the absence of IPTG, lane 3, extracts from strain PB198/pYtvA in the presence of IPTG (1 mM final concentration), both harvested 3 h after induction.

FIG. 3.

Effect of blue, red, and white light on the β-galactosidase activity of ytvA-overexpressing strain PB198/pYtvA. At time zero, cells were induced with 1 mM (end concentration) IPTG. Light intensities were 50 microeinsteins m⁻² s⁻¹ for standard white-light illumination and 30 microeinsteins m⁻² s⁻¹ for red- and blue-light illumination. Error bars indicate standard deviations calculated from two independent experiments, each with duplicate samples.