Fluorescent micrographs of N. viennensis EN76 microcolonies grown on floating filters. Micrographs of N. viennensis EN76 with an inoculum size of ~10⁷ cells on polycarbonate filter (A) before and (B) after 1 mM ammonia oxidation (refer to Fig. 1A) and (C) microcolonies of N. viennensis EN76 after oxidation of an additional 1 mM ammonia. (D) Microcolonies of N. viennensis EN76 with an inoculum size of ~10⁶ cells after 20 days of incubation (refer to Fig. 1A). The cells were stained with DAPI for 10 min and dried at 37°C on a glass slide.