FIG. 3.

Granule development supported by ciliates. Phase 1, formation of flocs. Ciliates settle on other organisms or particles (A). Bulky growth of ciliates (e.g., Epistylis sp.). Arrow indicates beginning colonization of ciliate stalks by bacteria (B). Phase 2, granule growth and core zone development. Zooids of the ciliates become completely overgrown by bacteria and die. Arrow marks limpid zooids of the ciliate colony. A dense core zone consisting of bacteria and the remains of ciliate stalks is formed in the center of the aggregates. Thereby, the cellular remnants of the ciliates act like a “backbone” (C). Phase 3, “mature” granule. Compact granules have formed. They can serve as a new substratum for swarming ciliate cells (D) settling on the granule surfaces (E).