Fig. 2: Engineering cell membrane permeability to facilitate PCA transport in S. oneidensis.
a Schematic of cell membrane permeability consisting of porin-mediated passive diffusion in the outer membrane (OM) and efflux pump-mediated active transport in the inner membrane (IM). b Maximum power density (taken from Supplementary Fig. 9) of strains SP1-SP6 and SP7-SP10. c NPN uptake assay to measure cell permeability (arb. units: arbitrary units). d Schematic of the intracellular PCA detector (pYYD-PsoxR-soxR-PsoxS-gfp) for evaluating cellular membrane permeability to PCA. The redox stress-responsive sensor PsoxR-soxR-PsoxS was employed to develop an intracellular PCA detector, comprising the effector protein SoxR and the SoxR-regulated promoter PsoxS. In PsoxR-soxR-PsoxS, the [2Fe-2S] cluster within SoxR dimer could be oxidized by PCA to activate the transcription of PsoxS. Upon exogenous introduction of PCA to a strain containing the PCA detector but lacking the PCA biosynthesis operon, the externally supplied PCA is transported into the cell, thereby activating GFP expression. This transport process is positively correlated with cellular membrane permeability. Consequently, cellular membrane permeability to PCA can be assessed by measuring the relative fluorescence intensity of GFP. e The relative fluorescence intensity of GFP. f The synthesized PCA level. g Cell growth profiles. h The viable cell number assessed from the dilution plate method. Results in (b–h) from three independent experiments (n = 3) were expressed as means and standard errors, and data in (b–h) are shown as the mean ± SD. The result (c) has been checked for consistency with 3 individual experiments. Source data are provided as a Source Data file.
