(164ag) Overexpression of Native Gene Presumably Encoding for D-Xylose Reductase in Escherichia coli leads to High Xylitol Production

Xylitol has a high global demand due to its wide-range application primarily in the food and pharmaceutical industries. Xylitol can also be utilized as a building block molecule for high-value chemical production. Currently, industrial xylitol production is through chemical synthesis involving catalytic hydrogenation of xylose. This process is expensive, requiring high energy expenditure and a series of purification steps thus affecting the market value of xylitol. Hence, biotechnological xylitol production emerges as a promising alternative to chemical synthesis. Bio-production of xylitol from D-xylose heavily relies on expression of heterologous xylose reductase (XR) that predominantly originates from yeasts, and some from filamentous fungi and bacteria into the host organisms. So far, there is no known native XR in Escherichia coli that catalyzes D-xylose to xylitol. Thus, it requires expression of heterologous XR from other organisms to produce xylitol. Surprisingly, plasmid-based overexpression of endogenous yahK gene in E. coli W3110 devoid of D-xylose isomerase pathway resulted in the production of xylitol as confirmed by GC-MSD and HPLC analysis. Using the said strain, high xylitol titer of 20.77 g/L (83% of theoretical yield) was produced via large-scale fermentation from D-xylose with glycerol as a co-substrate. Subsequently, an even higher yield of 30 g/L xylitol (100% of theoretical yield) was attained through whole-cell biocatalysis. So far, this study is the first to demonstrate xylitol production in E. coli using its native protein (YahK) suggesting the possibility of the presence of a silent xylose-oxidoreductase pathway (XORP) in E. coli. This work was supported by NRF funded by The Ministry of Science and ICT (2021R1F1A1045612), Basic Science Research Program through the Ministry of Education (2020R1A6A1A03038817).