Ammonia oxidation activities of N. viennensis EN76 and “N. chungbukensis” MY2 cells under different growth conditions. N. viennensis EN76 (A) and “N. chungbukensis” MY2 (B) with inoculum sizes of ~10⁶ cells and ~ 10⁷ cells, respectively, were used for the experiments. The subfigure in the upper right panel shows the specific growth rate (μ_max) under different culture conditions: 1 = filter without CaCO₃; 2 = filter with CaCO₃; 3 = liquid media without CaCO₃; 4 = inverted filter without CaCO₃. The symbols ^* and × indicate cultures for which growth rates cannot be calculated due to the absence of a log phase and no growth, respectively. All experiments were performed in triplicates. Data are presented as mean ± SD (n = 3), and the error bars are hidden when they are smaller than the width of the symbols. To avoid overlapping symbols, the value was shifted by −0.02 in (A) for the filter without CaCO₃ and by −0.09, 0.05, or 0.01 in (B) for the filter without CaCO₃, filter with CaCO₃, and inverted filter culture, respectively.