|Sakakibara, Yoshikiyo - NATL FOOD RES INSTITUTE|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 24, 2008
Publication Date: November 24, 2008
Citation: Sakakibara, Y., Saha, B.C. 2008. Microbial Production of Xylitol from L-arabinose by Metabolically Engineered Escherichia coli [abstract]. In: Proceedings of 4th Symposium of the International Society of Rare Sugars, November 21-24, 2008, Takamatsu, Kagawa, Japan. P. 64. Technical Abstract: Xylitol is used commercially as a natural sweetener in some food products such as chewing gum, soft drinks, and confectionery. It is currently produced by chemical reduction of D-xylose derived from plant materials, mainly hemicellulosic hydrolysates from birch trees. Expanding the substrate range is important for economically feasible production of xylitol from various raw materials. In particular, conversion of L-arabinose to xylitol should be useful for the efficient production of xylitol from hemicellulosic biomass hydrolysates because L-arabinose is the second most abundant pentose in them. An Escherichia coli strain, ZUC99(pATX210), that can produce xylitol from L-arabinose at a high yield has been created by introducing a new bioconversion pathway into cells. This pathway consists of three enzymes: L-arabinose isomerase, which converts L-arabinose to L-ribulose; D-psicose 3-epimerase, which conversts L-ribulose to L-xylulose; and L-xylulose reductase, which converts L-xylulose to xylitol. The genes encoding these enzymes were cloned behind the araBAD promoter in tandem so that they were polycistronically transcribed from the single promoter like an operon. Expression of the recombinant enzymes in the active form was successfully achieved in the presence of L-arabinose. Xylitol production profile of the recombinant strain was evaluated by shake-flask fermentation. ZUC99(pATX210) produced 2.6 g/L xylitol using 4.2 g/L L-arabinose with the xylitol yield of 0.62 g/g L-arabinose in 36 h. It was also determined that utilization of glycerol as a cosubstrate significantly improved the xylitol production and yield. In the presence of 11.8 g/L glycerol, ZUC99(pATX210) produced 9.7 g/L xylitol from 10.5 g/L L-arabinose with the xylitol yield of 0.92 g/g L-arabinose in 36 h. Furthermore, ZUC99(pATX210) exhibited the efficient conversion of L-arabinose to xylitol in fermentor experiments with 1 L medium containing glycerol. The strain produced 14.5 g/L xylitol using 15.2 g/L L-arabinose with the xylitol yield of 0.95 g/g L-arabinose in 30 h.