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Journal of Bacteriology, December 2001, p. 7037-7043, Vol. 183, No. 24
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.24.7037-7043.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Characterization of Xylanolytic Enzymes in Clostridium cellulovorans: Expression of Xylanase Activity Dependent on Growth Substrates

Akihiko Kosugi, Koichiro Murashima, and Roy H. Doi*

Section of Molecular and Cellular Biology, University of California, Davis, California 95616

Received 9 May 2001/Accepted 25 September 2001

Xylanase activity of Clostridium cellulovorans, an anaerobic, mesophilic, cellulolytic bacterium, was characterized. Most of the activity was secreted into the growth medium when the bacterium was grown on xylan. Furthermore, when the extracellular material was separated into cellulosomal and noncellulosomal fractions, the activity was present in both fractions. Each of these fractions contained at least two major and three minor xylanase activities. In both fractions, the pattern of xylan hydrolysis products was almost identical based on thin-layer chromatography analysis. The major xylanase activities in both fractions were associated with proteins with molecular weights of about 57,000 and 47,000 according to zymogram analyses, and the minor xylanases had molecular weights ranging from 45,000 to 28,000. High alpha -arabinofuranosidase activity was detected exclusively in the noncellulosomal fraction. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that cellulosomes derived from xylan-, cellobiose-, and cellulose-grown cultures had different subunit compositions. Also, when xylanase activity in the cellulosomes from the xylan-grown cultures was compared with that of cellobiose- and cellulose-grown cultures, the two major xylanases were dramatically increased in the presence of xylan. These results strongly indicated that C. cellulovorans is able to regulate the expression of xylanase activity and to vary the cellulosome composition depending on the growth substrate.

* Corresponding author. Mailing address: Section of Molecular and Cellular Biology, Division of Biological Sciences, University of California, One Shields Ave., Davis, CA 95616-8535. Phone: (530) 752-3191. Fax: (530) 752-3085. E-mail: rhdoi{at}ucdavis.edu.

Journal of Bacteriology, December 2001, p. 7037-7043, Vol. 183, No. 24
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.24.7037-7043.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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