An inducible AraC that responds to blue light instead of arabinose

In , the operon responsible for the catabolism of L-arabinose is regulated by the dimeric DNA-binding protein AraC. In the absence of L-arabinose, AraC binds to the distal I and O half-sites, leading to repression of the downstream P promoter. In the presence of the sugar, the dimer changes conformation and binds to the adjacent I and I half-sites, resulting in the activation of P. Here we engineer blue light-inducible AraC dimers in (BLADE) by swapping the dimerization domain of AraC with blue light-inducible dimerization domains. Using BLADE to overexpress proteins important for cell shape and division site selection, we reversibly control cell morphology with light. We demonstrate the exquisite light responsiveness of BLADE by employing it to create bacteriographs with an unprecedented quality. We then employ it to perform a medium-throughput characterization of 39 genes with poorly defined or completely unknown function. Finally, we expand the initial library and create a whole family of BLADE transcription factors (TFs), which we characterize using a novel 96-well light induction setup. Since the P promoter is commonly used by microbiologists, we envisage that the BLADE TFs will bring the many advantages of optogenetic gene expression to the field of microbiology.