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Journal of Bacteriology, April 2000, p. 1854-1863, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Capsule Biosynthesis and Basic Metabolism in Streptococcus pneumoniae Are Linked through the Cellular Phosphoglucomutase

Gail G. Hardy,dagger Melissa J. Caimano,Dagger and Janet Yother*

Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294

Received 22 November 1999/Accepted 17 January 2000

Synthesis of the type 3 capsular polysaccharide of Streptococcus pneumoniae requires UDP-glucose (UDP-Glc) and UDP-glucuronic acid (UDP-GlcUA) for production of the [3)-beta -D-GlcUA-(1right-arrow4)-beta -D-Glc-(1right-arrow]n polymer. The generation of UDP-Glc proceeds by conversion of Glc-6-P to Glc-1-P to UDP-Glc and is mediated by a phosphoglucomutase (PGM) and a Glc-1-P uridylyltransferase, respectively. Genes encoding both a Glc-1-P uridylyltransferase (cps3U) and a PGM homologue (cps3M) are present in the type 3 capsule locus, but these genes are not essential for capsule production. In this study, we characterized a mutant that produces fourfold less capsule than the type 3 parent. The spontaneous mutation resulting in this phenotype was not contained in the type 3 capsule locus but was instead located in a distant gene (pgm) encoding a second PGM homologue. The function of this gene product as a PGM was demonstrated through enzymatic and complementation studies. Insertional inactivation of pgm reduced capsule production to less than 10% of the parental level. The loss of PGM activity in the insertion mutants also caused growth defects and a strong selection for isolates containing second-site suppressor mutations. These results demonstrate that most of the PGM activity required for type 3 capsule biosynthesis is derived from the cellular PGM.

* Corresponding author. Mailing address: Department of Microbiology, BBRB 661, 845 19th St. S., University of Alabama at Birmingham, Birmingham, AL 35294. Phone: (205) 934-9531. Fax: (205) 975-6715. E-mail: jyother{at}uab.edu.

dagger Present address: Department of Pediatrics, Washington University, St. Louis, MO 63110.

Dagger Present address: Center for Microbial Pathogenesis, University of Connecticut Health Center, Farmington, CT 06030.

Journal of Bacteriology, April 2000, p. 1854-1863, Vol. 182, No. 7
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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