Ethanol ferrmentation of Kappaphycus alvarezii hydrolysates was performed using wild-type (WT) Saccharomyces cerevisiae CEN.PK2-1, hexokinase 2 deleted (Δhxk2) and adapted strain on high galactose concentrations. The WT and Δhxk2 strains produced 8.9 and 14.67 g/L of ethanol with yield coefficient (YEtOH) of 0.20 and 0.33 (g/g), respectively. However, neither the WT nor Δhxk2strain could utilize all of the galactose, leaving 16.4 and 6.2 g/L of galactose in the fermentation broth, respectively. Therefore, fermentation with S. cerevisiae CEN.PK2-1 adapted to galactose was carried out to increase the ethanol yield coefficient (YEtOH), producing a maximum ethanol concentration of 20.0 g/L with a YEtOH of 0.44 (g/g). Ethanol concentration of adapted strain was 1.36-2.25 times higher than WT and Δhxk2 strains. The adapted yeast exhibited the highest transcript levels of GAL genes. The yeast strain via adaptive yeast strain produced ethanol with a higher titer and yield due to a modular activation of GAL genes than WT or the hxk2 deleted strains.
Keywords: Adaptive evolution; CRISPR Cas-9; Fermentation; Kappaphycus alvarezii; Pretreatment.
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