Applied Biochemistry and Biotechnology, Vol.193, No.2, 335-348, 2021
Enhancement of Galactose Uptake fromKappaphycus alvareziiHydrolysate UsingSaccharomyces cerevisiaeThrough Overexpression of Leloir Pathway Genes
A total 42.68 g/L monosaccharide with 0.10 g/L HMF was obtained from 10% (w/v)Kappaphycus alvareziiwith thermal acid hydrolysis using 350 mM HNO(3)at 121 degrees C for 60 min and enzymatic saccharification with a 1:1 mixture of Viscozyme L and Celluclast 1.5 L for 72 h. To enhance the galactose utilization rate, fermentation was performed with overexpression ofGAL1(galactokinase),GAL7(galactose-1-phosphate uridyltransferase),GAL10(UDP-glucose-4-epimerase), andPGM2(phosphoglucomutase 2) inSaccharomyces cerevisiaeCEN.PK2 usingCCW12as a strong promoter. Among the strains, the overexpression ofPGM2showed twofold high galactose utilization rate (URgal) and produced ethanol 1.4-fold more than that of the control. Transcriptional analysis revealed the increase ofPGM2transcription level leading to enhance glucose-6-phosphate and fructose-6-phosphate and plays a key role in ensuring a higher glycolytic flux in thePGM2strain. This finding shows particular importance in biofuel production from seaweed because galactose is one of the major monosaccharides in seaweeds such asK.alvarezii.