Figure 2.

Coumarins from Arabidopsis root exudate improve biofilm formation of the soil bacterium B. subtilis. Structures of the coumarins Esculetin (A), Esculin (B), and Fraxetin (C) are depicted. The effect of these molecules (D, E, and F, respectively) in a B. subtilis pellicle assay conducted with a final concentration of 5 μM of each coumarin is shown. The sign (+) on the left side indicates coumarin treatment and the (−) sign indicates control (without coumarin). Bacterial cells were inoculated into the growth medium with different iron concentrations, and incubated at 23ºC for 2 days in dark before imaging. Biofilm formation appears as a bright layer in the positive wells. In low iron condition, root-derived coumarins improve B. subtilis biofilm formation.