Figure 1. Synthetic microbial ecosystem reveals spore germination in presence of mycelia in dry and oligotrophic environments.

(a) Scheme and photographs of the setup employed to carry out the germination, growth and labelling experiments. The synthetic ecosystem is comprised of two agar plugs serving as water and nutrient sources (‘with') for the fungi or the oomycete inoculated on top of one of the agar plugs. A silicon wafer free of water and nutrients (‘without') placed in the middle between the two ‘with' zones served as carrier for spores of B. subtilis. An air gap between the ‘with' and ‘without' zone prevented the diffusion of water or substrates to the spore region. (b) Gradual enlargement of bright-field micrographs of the silicon wafer overgrown by mycelium of P. ultimum. In close vicinity to the hyphae (black arrow) rod-shaped, vegetative bacterial cells (magenta arrows) were found, whereas smaller, round-shaped spores (yellow arrows) were located more distantly. (c) Fluorescence micrograph of the 4′,6-diamidine-2-phenylindol (DAPI)-stained wafer showing P. ultimum hyphae containing nuclei (white arrows) and vegetative cells as well as spores of B. subtilis.