Optogenetic Control of B. subtilis Gene Expression Using the CcaSR System.

Optogenetics enables precise control of gene expression in a variety of organisms. We recently developed the first system for optogenetic control of transcription in Bacillus subtilis. This system is based on CcaSR, a light-responsive two-component regulatory system originally derived from Synechocystis PCC 6803. The so-called B. subtilis CcaSR v1.0 enables activation of gene expression with green light and deactivation with red. As a result, B. subtilis CcaSR v1.0 can be used to program gene expression with high quantitative, spatial, and temporal resolution. The expression levels of the CcaS light sensing histidine kinase and the CcaR response regulator are set by the addition of chemical inducers in B. subtilis CcaSR v1.0, enabling adjustment of the basal expression level and optimization of the magnitude of gene expression induction. In principle, B. subtilis CcaSR v1.0 should be compatible with expression of any target gene of interest. Here, we provide growth, strain engineering, and light treatment protocols for working with B. subtilis CcaSR.