Image: EPS production by ammonia oxidisers at a high rate
Biofilm, aged 30,000 min (3 weeks). The contour lines show the oxygen concentration in mg/l. The image was rendered with POV-Ray, showing each cell as a sphere. The ammonia oxidisers ("Nitroso") are blue, and the EPS they produce is bluish (cyan); the nitrite oxidisers ("Nitro") are red. See the reaction scheme below. The grey box at the bottom is the inert substratum. Note the wrapped around boundaries in the horizontal direction. Scale: total width of the system = 200 µm.
At this high rate of EPS production, the producing cells spend more energy on EPS synthesis than they can gain from ammonia oxidation further down in the biofilm where they are oxygen limited. Hence, they begin to shrink and eventually die when they have shrunk below a minimum size. The EPS itself is assumed not to decay in the simulation shown here. Note how the red cells are dragged along with the stream of slime produced by the blue cells while the EPS hardly mixes with the clusters of red cells.
