Hyperexpression ofEscherichia coliXylose Isomerase

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Abstract
The xylose isomerase (xylA) structural gene was cloned under the control of the tac promoter and expressed in a xyl+ E. coli strain. Xylose isomerase accounted for approximately 28% of the total cell protein when this tac-xylA fusion was induced with isopropylthio β-D-galactopyranoside. Hyperexpression of the xylA gene inhibited xylose utilization. E. coli carrying this tac-xylA fusion was encapsulated in calcium-alginate beads and used to isomerase xylose in a column reactor. Conversion of xylose to xylulose was 3–4% with a residence time in the column of 2 minutes and a maximum of 12% upon recycling.