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Applied and Environmental Microbiology, September 2009, p. 5743-5749, Vol. 75, No. 18
0099-2240/09/$08.00+0     doi:10.1128/AEM.01180-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Genetic Engineering of Enterobacter asburiae Strain JDR-1 for Efficient Production of Ethanol from Hemicellulose Hydrolysates{triangledown}

Changhao Bi, Xueli Zhang, Lonnie O. Ingram, and James F. Preston*

Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611

Received 21 May 2009/ Accepted 11 July 2009

Dilute acid pretreatment is an established method for hydrolyzing the methylglucuronoxylans of hemicellulose to release fermentable xylose. In addition to xylose, this process releases the aldouronate methylglucuronoxylose, which cannot be metabolized by current ethanologenic biocatalysts. Enterobacter asburiae JDR-1, isolated from colonized wood, was found to efficiently ferment both methylglucuronoxylose and xylose in acid hydrolysates of sweet gum xylan, producing predominantly ethanol and acetate. Transformation of E. asburiae JDR-1 with pLOI555 or pLOI297, each containing the PET operon containing pyruvate decarboxylase (pdc) and alcohol dehydrogenase B (adhB) genes derived from Zymomonas mobilis, replaced mixed-acid fermentation with homoethanol fermentation. Deletion of the pyruvate formate lyase (pflB) gene further increased the ethanol yield, resulting in a stable E. asburiae E1(pLOI555) strain that efficiently utilized both xylose and methylglucuronoxylose in dilute acid hydrolysates of sweet gum xylan. Ethanol was produced from xylan hydrolysate by E. asburiae E1(pLOI555) with a yield that was 99% of the theoretical maximum yield and at a rate of 0.11 g ethanol/g (dry weight) cells/h, which was 1.57 times the yield and 1.48 times the rate obtained with the ethanologenic strain Escherichia coli KO11. This engineered derivative of E. asburiae JDR-1 that is able to ferment the predominant hexoses and pentoses derived from both hemicellulose and cellulose fractions is a promising subject for development as an ethanologenic biocatalyst for production of fuels and chemicals from agricultural residues and energy crops.

* Corresponding author. Mailing address: Department of Microbiology and Cell Science, University of Florida, Bldg. 981, Museum Rd., Gainesville, FL 32611-0700. Phone: (352) 392-5923. Fax: (352) 392-5922. E-mail: jpreston{at}ufl.edu

{triangledown} Published ahead of print on 17 July 2009.

Applied and Environmental Microbiology, September 2009, p. 5743-5749, Vol. 75, No. 18
0099-2240/09/$08.00+0     doi:10.1128/AEM.01180-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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