Capsule biosynthesis and basic metabolism in Streptococcus pneumoniae are linked through the cellular phosphoglucomutase.
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-(1-->4)-beta-D-Glc-(1-->](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.
Hardy
G G
GG
Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Caimano
M J
MJ
Yother
J
J
D000595:Amino Acid Sequence; D016667:Bacterial Capsules / Q000096:biosynthesis* / Q000235:genetics; D001483:Base Sequence; D002455:Cell Division; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000201:enzymology; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D010733:Phosphoglucomutase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D013296:Streptococcus pneumoniae / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D013489:Suppression, Genetic / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics
D012333:RNA, Messenger; D010733:Phosphoglucomutase