Fig. 1

A Schematic representation of the plasmid-based pSenHis biosensor for intracellular detection of l-histidine in C. glutamicum. In the presence of elevated intracellular concentrations of l-histidine, the transcriptional activator LysG-A219L binds l-histidine and binds to its target promoter P_lysE to activate the expression of the eyfp gene encoding for the fluorescent reporter protein EYFP leading to fluorescent single cells. B Increased fluorescence response of single l-histidine-producing C. glutamicum CgHis2 cells during FACS upon supplementation of different His-Ala dipeptide concentrations. 0, 3, 10, and 30 mM l-His-l-Ala dipeptides were added to microtiter plate cultivations of C. glutamicum CgHis2 in defined CGXII medium with 2% d-glucose. In the middle of the exponential growth phase (after 6 h of cultivation), fluorescence intensities of 100,000 cells of each culture were analyzed by FACS. The depicted distributions represent standard deviations of the mean from three independent technical replicates showing the cell count at respective eYFP fluorescence (arbitrary units)