Cofermentation of Glucose, Xylose, and Arabinose by Genomic DNA-lntegrated Xylose/Arabinose Fermenting Strain of Zymomonas mobilis AX101

Abstract

Cofermentation of glucose, xylose, and arabinose is critical for complete bioconversion of lignocellulosic biomass, such as agricultural residues and herbaceous energy crops, to ethanol. We have previously developed a plas-mid-bearing strain of Zymomonas mobilis (206C[pZB301]) capable of cofer-menting glucose, xylose, and arabinose to ethanol. To enhance its genetic stability, several genomic DNA—integrated strains of Z. mobilis have been developed through the insertion of all seven genes necessay for xylose and arabinose fermentation into the Zymomonas genome. From all the integrants developed, four were selected for further evaluation. The integrants were tested for stability by repeated transfer in a nonselective medium (containing only glucose). Based on the stability test, one of the integrants (AX101) was selected for further evaluation. A series of batch and continuous fermentations was designed to evaluate the cofermentation of glucose, xylose, and L-arabinose with the strain AX101. The pH range of study was 4.5, 5.0, and 5.5 at 30°C The cofermentation process yield was about 84%, which is about the same as that of plasmid-bearing strain 206C(pZB301). Although cofermentation of all three sugars was achieved, there was a preferential order of sugar utilization: glucose first, then xylose, and arabinose last.