Increasing NADPH Availability for Xylitol Production via Pentose-Phosphate-Pathway Gene Overexpression and Embden–Meyerhof–Parnas-Pathway Gene Deletion in <i>Escherichia coli</i>
Xinsong Yuan, Yudi Mao, Shuai Tu, Jianping Lin, Huahao Shen, Lirong Yang, Mianbin Wu
Abstract
Cofactor availability is often a rate-limiting factor in the bioconversion of xylose to xylitol. The overexpression of pentose phosphate pathway genes and the deletion of Embden–Meyerhof–Parnas pathway genes can modulate the glucose metabolic flux and increase the intracellular NADPH supply, enabling Escherichia coli cells to produce xylitol from corncob hydrolysates. The effects of zwf and/or gnd overexpression and pfkA, pfkB, and/or pgi deletion on the intracellular redox environment and xylitol production were examined. The NADPH-enhanced strain 2bpgi produced 162 g/L xylitol from corncob hydrolysates after a 76 h fed-batch fermentation in a 15 L bioreactor, which was 13.3% greater than the 143 g/L xylitol produced by the IS5-d control strain. Additionally, the xylitol productivity and xylitol yield per glucose for 2bpgi were 2.13 g/L/h and 2.50 g/g, respectively. Thus, the genetic modifications in 2bpgi significantly enhanced NADPH regeneration, making 2bpgi a potentially useful strain for the industrial-scale production of xylitol from detoxified corncob hydrolysates.