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Applied and Environmental Microbiology, April 2001, p. 1445-1452, Vol. 67, No. 4
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.4.1445-1452.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Genetic Evidence for a Defective Xylan Degradation Pathway in Lactococcus lactis

Karn A. Erlandson,dagger Soazig C. Delamarre, and Carl A. Batt*

Department of Food Science, Cornell University, Ithaca, New York 14853

Received 21 June 2000/Accepted 4 January 2001

Genetic and biochemical evidence for a defective xylan degradation pathway was found linked to the xylose operon in three lactococcal strains, Lactococcus lactis 210, L. lactis IO-1, and L. lactis NRRL B-4449. Immediately downstream of the xylulose kinase gene (xylB) (K. A. Erlandson, J.-H. Park, W. El Khal, H.-H. Kao, P. Basaran, S. Brydges, and C. A. Batt, Appl. Environ. Microbiol. 66:3974-3980, 1999) are two open reading frames encoding a mutarotase (xylM) and a xyloside transporter (xynT) and a partial open reading frame encoding a beta -xylosidase (xynB). These are functions previously unreported for lactococci or lactobacilli. The mutarotase activity of the putative xylM gene product was confirmed by overexpression of the L. lactis enzyme in Escherichia coli and purification of recombinant XylM. We hypothesize that the mutarotase links xylan degradation to xylose metabolism due to the anomeric preference of xylose isomerase. In addition, Northern hybridization experiments suggested that the xylM and xynTB genes are cotranscribed with the xylRAB genes, responsible for xylose metabolism. Although none of the three strains appeared to metabolize xylan or xylobiose, they exhibited xylosidase activity, and L. lactis IO-1 and L. lactis NRRL B-4449 had functional mutarotases.

* Corresponding author. Mailing address: Cornell University, Department of Food Science, 312 Stocking Hall, Ithaca, NY 14853. Phone: (607) 255-2896. Fax: (607) 255-8741. E-mail: cab10{at}cornell.edu.

dagger Present address: Procter and Gamble Corporation, Cincinnati, Ohio.

Applied and Environmental Microbiology, April 2001, p. 1445-1452, Vol. 67, No. 4
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.4.1445-1452.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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