Fig. 3

Investigation of genotype and aeration conditions for 2,3-BDO production by the YPH499 wild-type strain. Ec, Escherichia coli; Lp, Lactobacillus plantarum; Tf, Thermobifida fusca. Op, codon-optimized. Fermentations were performed in test tubes containing 3 mL of SD selection medium (20 g L⁻¹ glucose) under the indicated aeration conditions. The concentrations of 2,3-BDO and ethanol in the media were determined at 48 h after the start of fermentation. a 2,3-BDO production by YPH499 strains expressing high-activity ALSs (black bars; YIDB022–025) under semi-aerobic conditions (150 rpm, aluminum cap). A truncated version of the ILV2 gene (ILV2c), which is expressed in the cytosol, was used as a comparative yeast ALS (gray bars). YPH499 harboring the mock vector was used as the negative control (white bars). b Effect of aeration on 2,3-BDO production by YPH499 strain expressing high-activity ALS (alsLpOp gene; YIDB025). The agitation speed (150 rpm) was increased to 300 rpm and the cover cap on the test tube was changed from an aluminum cap to a vent-type cap to increase the aeration. The gray bars indicate the baseline (former) conditions (150 rpm, aluminum cap) and the black bars indicate the altered conditions (300 rpm, aluminum or vent-type cap). c 2,3-BDO production by YPH499 strains co-expressing high-activity ALS (alsLpOp gene) and yeast endogenous BDH (BDH1 gene) (black bars; YIDB034) under aerobic conditions (300 rpm, aluminum cap). YPH499 expressing only the ALS (alsLpOp) gene was used as the comparative control (gray bars). The YPH499 wild-type strain was used as the negative control (white bars). Data are, respectively, presented as the mean ± standard deviation of three independent transformants (for a and c) and of three separate cultivations (for b) (n = 3 each). Statistical significance was assessed by the t test (*p < 0.05)