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Applied and Environmental Microbiology, January 2009, p. 395-404, Vol. 75, No. 2
0099-2240/09/$08.00+0     doi:10.1128/AEM.01941-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Complete Fermentation of Xylose and Methylglucuronoxylose Derived from Methylglucuronoxylan by Enterobacter asburiae Strain JDR-1

Changhao Bi, John D. Rice, and James F. Preston^*

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

Received 20 August 2008/ Accepted 8 November 2008

Acid pretreatment is commonly used to release pentoses from the hemicellulose fraction of cellulosic biomass for bioconversion. The predominant pentose in the hemicellulose fraction of hardwoods and crop residues is xylose in the polysaccharide methylglucuronoxylan, in which as many as one in six of the β-1,4-linked xylopyranose residues is substituted with -1,2-linked 4-O-methylglucuronopyranose. Resistance of the -1,2-methylglucuronosyl linkages to acid hydrolysis results in release of the aldobiuronate 4-O-methylglucuronoxylose, which is not fermented by bacterial biocatalysts currently used for bioconversion of hemicellulose. Enterobacter asburiae strain JDR-1, isolated from colonized hardwood (sweetgum), efficiently ferments both methylglucuronoxylose and xylose, producing predominantly ethanol and acetate. ¹³C-nuclear magnetic resonance studies defined the Embden-Meyerhof pathway for metabolism of glucose and the pentose phosphate pathway for xylose metabolism. Rates of substrate utilization, product formation, and molar growth yields indicated methylglucuronoxylose is transported into the cell and hydrolyzed to release methanol, xylose, and hexauronate. Enterobacter asburiae strain JDR-1 is the first microorganism described that ferments methylglucuronoxylose generated along with xylose during the acid-mediated saccharification of hemicellulose. Genetic definition of the methylglucuronoxylose utilization pathway may allow metabolic engineering of established gram-negative bacterial biocatalysts for complete bioconversion of acid hydrolysates of methylglucuronoxylan. Alternatively, Enterobacter asburiae strain JDR-1 may be engineered for the efficient conversion of acid hydrolysates of hemicellulose to biofuels and chemical feedstocks.

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

Published ahead of print on 14 November 2008.

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Applied and Environmental Microbiology, January 2009, p. 395-404, Vol. 75, No. 2
0099-2240/09/$08.00+0     doi:10.1128/AEM.01941-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Bi, C., Zhang, X., Ingram, L. O., Preston, J. F. (2009). Genetic Engineering of Enterobacter asburiae Strain JDR-1 for Efficient Production of Ethanol from Hemicellulose Hydrolysates. Appl. Environ. Microbiol. 75: 5743-5749 [Abstract] [Full Text]  
• Nong, G., Rice, J. D., Chow, V., Preston, J. F. (2009). Aldouronate Utilization in Paenibacillus sp. Strain JDR-2: Physiological and Enzymatic Evidence for Coupling of Extracellular Depolymerization and Intracellular Metabolism. Appl. Environ. Microbiol. 75: 4410-4418 [Abstract] [Full Text]