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Journal of Bacteriology, November 2008, p. 7219-7231, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.01003-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Characterization of the Caulobacter crescentus Holdfast Polysaccharide Biosynthesis Pathway Reveals Significant Redundancy in the Initiating Glycosyltransferase and Polymerase Steps{triangledown}

Evelyn Toh,1 Harry D. Kurtz Jr.,2 and Yves V. Brun1*

Department of Biology, Indiana University, Bloomington, Indiana 47405-3700,1 Department of Genetics and Biochemistry, 100 Jordan Hall, Clemson University, Clemson, South Carolina 296342

Received 21 July 2008/ Accepted 25 August 2008

Caulobacter crescentus cells adhere to surfaces by using an extremely strong polar adhesin called the holdfast. The polysaccharide component of the holdfast is comprised in part of oligomers of N-acetylglucosamine. The genes involved in the export of the holdfast polysaccharide and the anchoring of the holdfast to the cell were previously discovered. In this study, we identified a cluster of polysaccharide biosynthesis genes (hfsEFGH) directly adjacent to the holdfast polysaccharide export genes. Sequence analysis indicated that these genes are involved in the biosynthesis of the minimum repeat unit of the holdfast polysaccharide. HfsE is predicted to be a UDP-sugar lipid-carrier transferase, the glycosyltransferase that catalyzes the first step in polysaccharide biosynthesis. HfsF is predicted to be a flippase, HfsG is a glycosyltransferase, and HfsH is similar to a polysaccharide (chitin) deacetylase. In-frame hfsG and hfsH deletion mutants resulted in severe deficiencies both in surface adhesion and in binding to the holdfast-specific lectin wheat germ agglutinin. In contrast, hfsE and hfsF mutants exhibited nearly wild-type levels of adhesion and holdfast synthesis. We identified three paralogs to hfsE, two of which are redundant to hfsE for holdfast synthesis. We also identified a redundant paralog to the hfsC gene, encoding the putative polysaccharide polymerase, and present evidence that the hfsE and hfsC paralogs, together with the hfs genes, are absolutely required for proper holdfast synthesis.

* Corresponding author. Mailing address: Department of Biology, Indiana University, Bloomington, Indiana 47405-3700. Phone: (812) 855-8860. Fax: (812) 855-6705. E-mail: ybrun{at}indiana.edu

{triangledown} Published ahead of print on 29 August 2008.

Journal of Bacteriology, November 2008, p. 7219-7231, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.01003-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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