Fig. 1: Sucrose promotes root colonization and solid surface motility (SSM) by B. subtilis.

A LSCM images of 18-day-old tomato roots observed 72 h after inoculation with a B. subtilis 3610 derivative constitutively expressing mKate2 and treated with different sugars (Fru fructose, Glc glucose, Mal maltose, and Suc sucrose). For treatments of sugars, 5 ml cell suspension supplemented with 0.5% (w/v) sugar was applied to the roots. Water indicates the same volume of water replacing any sugar solution. CK indicates no addition of bacterial cells and sugars. Shown pictures are representatives of at least 20 independent root samples (scale bars: 50 μm). B The influence of different sugar supplementations on the colonization of 3610 cells on tomato roots was determined by counting colony forming unit (CFU) per mm root length. Error bars represent standard deviations. * indicates p value < 0.05; ** indicates p value < 0.01; NS no statistical difference. C The concentration of supplementary sucrose positively correlated with the robustness of solid-surface movement (SSM) by 3610. The microscopic images of outer-edge cells stained with flagella-specific dye, on solid LB plate with or without sucrose (5 g/L). Pictures are representatives of at least five independent samples (scale bars: 3 μm). D The increasing concentrations of agar negatively influenced the robustness of sucrose-induced SSM. E Colony expanding rate of 3610 on solid LB plate with or without supplementary sucrose (5 g/L) was determined by measuring the diameter of the colony periodically. Assays were done in triplicate. Error bars represent standard deviations. F Addition of sucrose (5 g/L) also triggered SSM by other Bacillus strains on solid LB plates. All Petra dishes shown here have a diameter of 10 cm.