Figure 5. Spatial organization of consortium on rough porous surfaces.

Consortium of strains PpF4 and PpF107 were grown on a porous surface model (PSM). The PSM consisted of a saturated ceramic disc (a, red arrowhead) connected with tubing to a medium reservoir (b). A prescribed suction was applied to the porous surface by lowering the position of the medium reservoir relative to the ceramic surface (b). This suction mimics the retention of liquid on soil surfaces by matric forces, which is commonly defined as water matric potential (expressed as a negative pressure in kPa). Lower matric potential values thus correspond to drier conditions and result in thinner and more disconnected liquid films on the rough surface. (c) Micrograph shows the PSM hydrated surface at near saturation conditions (−0.5 kPa), which is made of connected liquid films of various thicknesses depending on the surface geometry. Droplets (0.5 μl) of PpF4:PpF107 suspension (mixed 1:1) with OD₆₀₀ adjusted to 1.0 (≈100,000 cells) were pipetted onto the center of the PSMs (inoculation diameter ≈3 mm). Consortium was grown during 5 days at room temperature, under ‘wet’ conditions (matric potential value of −0.5 kPa) or under drier conditions (−2 kPa). The only carbon and energy source available to the consortium was either toluene provided in the gas phase (d,e) or benzoate provided in the medium at 10 mM concentration (f,g). Results from exemplary experiments are shown, with overlay images of PpF4 and PpF107 tagged with respectively eGFP (shown as pseudo-color cyan) and mCherry (shown as pseudo-color magenta). (e,g) Close-ups from d and f (rectangles) showing patterns of strains. Growth is faster with benzoate, and after 5 days under wet conditions the whole PSM surface is colonized (f).