Plackett-Burman experimental design for screening of the culture conditions.

aA, NH4Cl (mM); B, Fructose (mM); C, Pyruvate (mM); D, L-Aspartic acid (mM); E, Arginine (mM); F, MgSO4 (mM); G CaCl2 (mM); H, K2HPO4 (mM); I, HEPES (mM); J, EDTA-Fe3+ (mM); K, FeSO4 (mM); L, CuSO4 (mM); M, ZnSO4(mM); N, TES (ml); O, Inoculation size (×106 cells/ml); P, pH control (NaHCO3 (−1), NH4HCO3 (+1)); Q, Agitation speed (rpm); R, Temperature (°C); S, Time (h).bCB, Biomass concentration (×108 cells/ml); YN, Nitrite yield (mg/mg); RA, Ammonium removal (%).All experiments were performed in triplicate. Each response was represented as mean ± SD (n = 3).