Image: Capsule formation 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 capsules surrounding them are 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.
As with EPS production at a high rate, producing cells shrink and eventually die in the deep end of the biofilm where not enough oxygen penetrates to sustain the energy expenditure of EPS production. Since capsules are EPS material that stays attached to the cells, cells become more evenly separated from each other compared with EPS production.
