Methylammonium transport of yeast strain MLY131a/α (mep1-3Δ) transformed with Geosiphon pyriformis AMTs. (A) Concentration-dependent [14C]methylammonium uptake of yeast cells transformed with empty vector (negative control), ScMEP1 (positive control), GiAMT1, GpAMT1, or GpAMT2. ScMep1, Km = 40.0 μM, Vmax = 3.5 nmol min−1 for 109 cells; GiAMT1, Km = 11.1 μM, Vmax = 1.3 nmol min−1 for 109 cells. Error bars, ±standard deviation; n = 3 to 6 biological replicates. (B) Growth of the same transformants in buffered liquid medium containing 0.1% proline as sole nitrogen source and different concentrations of cytotoxic methylammonium. Error bars, ±standard deviation; n = 6 biological replicates. Different letters above bars indicate highly significant differences (P ≤ 0.001, ANOVA test) between pairwise comparisons.