Fig. 2: Surfactin mediates sucrose-induced SSM by B. subtilis.
From: Sucrose triggers a novel signaling cascade promoting Bacillus subtilis rhizosphere colonization
A The effect of various sugars on surfactin yield (µg/cm2) by B. subtilis 3610 cells was assayed on solid LB agar plates (1.5% agar, w/v). Samples were collected from the plates supplemented with different sugars, all at the concentration of 5 g/L. Surfactin was extracted, and the amount of surfactin was determined by HPLC as described in the method. The error bars represent standard deviations from triplicate assays. * indicates p value < 0.05; ** indicates p value < 0.01; NS no statistical difference. B Microscopy images of cells harboring the promoter fusion (PsrfAA-gfp, CY106) collected from the edge of the colonies after 4 h of inoculation on solid LB plates with or without 5 g/L sucrose (scale bars: 5 μm). C Quantification of fluorescence intensity of the cells expressing PsrfAA-gfp from above. The quantification for each sample is based on roughly 200 cells by using ImageJ. Solid lines in the middle indicates the mean value (artificial units, AU) of the fluorescence intensity. Upper and lower dotted lines indicate the 75% and 25% quartile, respectively. D Assays of β-galactosidase activities of cells bearing the PsrfAA-lacZ promoter fusion (KG203). Cells were similarly collected from the edge of the colonies after 4 h inoculation from solid LB agar plates without sugar addition, with the addition of 5 g/L sucrose or glucose. Assays were done in biological triplicates. Error bars represent standard deviations. ** indicates p value < 0.01; NS, no statistical difference. E The srfAA mutants of three B. subtilis strains (9407, NCD-2, and 3610) lost SSM on solid LB with 5 g/L sucrose plates when compared to their wild-type counterparts. Images are representatives of at least 3 independent assays. F Pure surfactin, but not sucrose, rescues the phenotype of SSM and hyper-flagellation in a srfAA mutant of 3610 (Tm01). Solutions (in a volume of 100 μL) containing 180 μg surfactin were filled into an Oxford-cup, which is 1 cm away from the inoculating spot with the B. subtilis cells. All Petra dishes shown here have a diameter of 10 cm.
