Fig. 2.
Nystatin and surfactin stimulate transcription of yqxM operon in a subpopulation of cells by inducing potassium leakage. (A) Schematic representation of the signaling pathway leading to matrix production. Spo0A is activated by phosphorylation and induces the expression of SinI, which antagonizes the repressor SinR. Once SinR is antagonized, the eps and yqxM operons are derepressed. (B) β-Galactosidase assay monitoring the expression of the yqxM operon using the transcriptional fusion PyqxM-lacZ. (C) Overlay of fluorescence (yellow) and transmitted light (gray) micrographs of WT B. subtilis harboring PyqxM-yfp. (Scale bar: 3 μm.) (D) Flow cytometry analysis of WT cells harboring PyqxM-yfp, untreated and in the presence of nystatin or surfactin. Untreated control cells that do not harbor any yfp gene show a single population of cells with very low relative fluorescence due to background. Cells harboring PyqxM-yfp fusion also show a single population but with slightly higher fluorescence (blue peak). In contrast, treatment with nystatin or surfactin (green and orange graphs, respectively) results in the appearance of a subpopulation of cells with high relative fluorescence, seen as the shoulder to the right of the main peaks.