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Title: Microbial Production of Xylitol from L-arabinose by Metabolically Engineered Escherichia coli

item Saha, Badal

Submitted to: Journal of Bioscience and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/25/2008
Publication Date: 2/1/2009
Citation: Sakakibara, Y., Saha, B.C., Taylor, P. 2009. Microbial Production of Xylitol from L-arabinose by Metabolically Engineered Escherichia coli. Journal of Bioscience and Bioengineering. 107(5):506-511.

Interpretive Summary: Microbial production of xylitol (a low calorie anticariogenic sweetener) using both pentose (five carbon) sugars (xylose, arabinose) derived from agricultural residues is attractive for reducing its manufacturing cost. Some yeasts can produce xylitol from xylose but they also produce arabitol from arabinose. It is difficult to separate xylitol and arabitol. In this study, a recombinant bacterial strain has been created that produces xylitol from arabinose without making arabitol. The research will help to develop a recombinant bacterium that can produce xylitol from both pentose sugars.

Technical Abstract: An Escherichia coli strain, ZUC99(pATX210), which 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 converts 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 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. ZUC99(pATX210) also exhibited the efficient conversion in fermentor experiments with 1 l medium containing L-arabinose and glycerol. The strain produced 14.5 g/l xylitol from 15.2 g/l L-arabinose with the xylitol yield of 0.95 g/g L-arabinose in 30 h.