Figure 3

Variation in Gdh1p expression provides different growth trends in high and low ammonia environments. (A) Flow cytometry histograms of two GDH1 promoter mutants exhibiting different noise and similar abundance profiles in Gdh1p as the wildtype strain. The 'high noise' mutant has a square of the coefficient of variation (σ²/p²) of 0.74 (20% higher than wildtype) and the 'low noise' mutant has a σ²/p² of 0.56 (10% lower than wildtype). (B) The high noise mutant exhibits greater resistance to ammonia stress under high ammonia concentrations. The fold change in CFUs is reported at different time points following exposure to high ammonia (600 mM) media using the plate-based fitness assays. Dashed line, wildtype; gray line, high noise strain; black line, low noise strain. (C) The high noise mutant exhibits greater delayed toxicity to ammonia stress under high ammonia and low potassium concentrations. The fold change in CFUs is reported at different time points following exposure to high ammonia (600 mM) and low potassium (17 mM) media. Dashed line, wildtype; gray line, high noise strain; black line, low noise strain. (D) The low noise mutant exhibits greater fitness in low ammonia environments. Fitness for the high and low noise strains were measured across a range of low ammonia concentrations using the competition fitness assays. Fitness is reported as the natural log of the change in frequency over the growth period relative to the wildtype strain. Black circles, low noise strain; gray circles, high noise strain.