Fig. 1: Architecture and characterization of plasmid systems for red-light-controlled gene expression in bacteria.

a Bacteriophytochromes (BphP) possess N-terminal photosensory modules (PSM) which covalently bind biliverdin (BV) chromophores and comprise consecutive PAS, GAF, and PHY domains. As exemplified for the BphP from Deinococcus radiodurans, the C-terminal effector module is most often a sensor histidine kinase consisting of DHp (dimerization and histidine phosphotransfer) and CA (catalytic and ATP-binding) domains. b In the pREDusk circuits, the LacI^q promoter controls the expression of a tricistronic operon comprising a heme oxygenase (HO), a sensor histidine kinase (SHK) (i.e., DrF1 or DmF1), and the response regulator (RR) FixJ from Bradyrhizobium japonicum. DmF1 and DrF1 consist of the PSM from the Deinococcus maricopensis and D. radiodurans BphPs, respectively, linked to the effector module of the B. japonicum FixL SHK. In darkness, DmF1/DrF1 drive FixJ phosphorylation and thereby activate expression of a gene of interest (GOI) from the FixK2 promoter. The pREDawn system extends pREDusk by an additional λ phage cI repressor and its target promoter pR, which induces inversion and amplification of the circuit response to red light. c DsRed production of bacteria harboring DmREDusk (green circles) or DrREDusk (orange circles) as a function of red-light intensity. Fluorescence readings were normalized to the optical density of the bacterial cultures at 600 nm (OD₆₀₀) and corrected for background fluorescence. Data represent mean ± s.d. of n = 3 biologically independent replicates and were normalized to DmREDusk in darkness. Light intensities are averaged over the duty cycle as marked by angled brackets. d As c but for DmREDawn (green squares) and DrREDawn (orange squares). e Analysis by flow cytometry of bacteria carrying DmREDusk (top) or DrREDusk (bottom) and incubated under red light (red) or in darkness (gray). The yellow curves denote control bacteria harboring empty vectors with a multiple-cloning site replacing DsRed. n = 3 biologically independent replicates for each sample are shown. f As panel e but for DmREDawn and DrREDawn. Source data are provided as a Source Data file.