FIG. 2.

Effect of FDH1 and FDH2 deletions on residual formate levels in anaerobic conditions, using galactose as a carbon source. Liquid cultures of S. cerevisiae were grown under pH-buffered or unbuffered conditions with different initial formate concentrations. (A) 1 mM initial formate, pH buffered; (B) 1 mM initial formate, no pH buffering; (C) 20 mM initial formate, pH buffered; (D) growth curves of pH-buffered experiments. The inset depicts the growth on a logarithmic scale. When pH buffering was used, final values reached 6.35 ± 0.05, starting from a pH of 6.5. Final pH values without buffering reached 3.5 ± 0.1. ○, PSY580a (wild type) with 1 mM initial formate; □, PSY3646 (ΔFDH1 ΔFDH2) with 1 mM initial formate; •, PSY580a with 20 mM initial formate; ▪, PSY3646 with 20 mM initial formate. The dashed line indicates no pH buffering. The growth rates of both strains in 1 mM initial formate were almost identical: hence the overlap in panel D. The error bars indicate standard deviations of three replicates.