NoAttachment

Video S1: Simulation of a root tip entering a patch of bacteria using Smooth Particle Hydrodynamic (SPH) approach. Attached bacteria on the root surface (red circle) move slowly away from the tip, and this results in an accumulation of bacteria at the root tip observed experimentally. Free bacteria (blue circle) in soil however move away from the tip at constant velocity. Free bacteria grow less because they can’t remain at the root tip. Graphs below the rhizosphere model indicate bacterial density for attached bacteria (red) free moving bacteria (blue) and carbon concentration (green).

 

EffectOfAttachment short

Video S2: Effect of microbial attachment bacteria density. The effect of attachment can be visualised by activating attachment once the steady state without attachment is observed. This produce a drastic increase in the density of attached bacteria with a very small decrease in the density of free moving bacteria. Overall, the total density of bacteria in the root tip is increased 

 without cap        with cap

Video S3: Bacterial density in response to exposure to bacteria during a short period of time. In the absence of root cap (left) all bacteria disappear. When a root cap is acting as a reservoir (right) bacterial density maintains in low quantity at the root tip

 

Chemotaxis

Video S4: Simulation of a root tip entering a patch of bacteria with high chemotactic coefficient. At first contact with the root, bacterial velocity is lower than root tip velocity and bacteria are displaced away from the tip. However, after about 60 to 80 h spent in contact with the root tip, the bacterial population attain a critical size and progress towards the root tip. A bacterial front is formed and its profile is similar to a supersonic booms. At steady state, the front is placed in the elongation zone and corresponds to the peak of carbon density. Graphs below the rhizosphere model indicate the equivalent bacterial density for free moving bacteria (blue) and carbon concentration (green).