(A) Strong expression of secreted invertase allows growth from a single cell at low sucrose concentrations. All GAL1 promoter induction data is from the same yeast strain yJHK312 in which transcription of SUC2 is driven by the GAL1 promoter. Galactokinase (GAL1) is deleted from this strain so that galactose acts as an inducer and not as a carbon source, and the Gal regulon has been engineered to produce a graded rather than a bistable response to increased galactose concentrations by overexpressing GAL3 from the ACT1 promoter (Ingolia and Murray, 2007). (B) Sucrose import allows growth from a single cell in low sucrose concentrations. The ‘SUC2, import' strain yJHK372 expresses SUC2 from the SUC2 promoter and MAL11 from the ACT1 promoter. The ‘SUC2, no import' strain yJHK222 expresses SUC2 from the SUC2 promoter. The ‘suc2-1cyt, import' strain yJHK373 expresses cytoplasmic invertase from the SUC2 promoter and MAL11 from the ACT1 promoter. The ‘suc2Δ, import' strain yJHK374 has SUC2 deleted and expresses MAL11 from the ACT1 promoter. For both (A) and (B), single cells were inoculated by fluorescence activated cell sorting (FACS) into 150 µl wells at the given sugar and galactose concentration and grown without shaking for 85 hr at 30°C and the results shown are totals of three experiments; each experiment used one plate per sugar concentration, and each plate used 24 wells per strain or galactose concentration. In both figures, 2 mM glucose + 2 mM fructose is used as a positive control, and error bars refer to 95% binomial confidence interval using the adjusted Wald method. FRU is fructose, GLC is glucose, and SUC is sucrose.