Genetic Relatedness of theStreptococcus pneumoniaeCapsular Biosynthetic Loci

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Abstract
Streptococcus pneumoniae(the pneumococcus) produces 1 of 91 capsular polysaccharides (CPS) that define the serotype. Thecpsloci of 88 pneumococcal serotypes whose CPS is synthesized by the Wzy-dependent pathway were compared with each other and with additional streptococcal polysaccharide biosynthetic loci and were clustered according to the proportion of shared homology groups (HGs), weighted for the sequence similarities between the genes encoding the shared HGs. Thecpsloci of the 88 pneumococcal serotypes were distributed into eight major clusters and 21 subclusters. All serotypes within the same serogroup fell into the same major cluster, but in six cases, serotypes within the same serogroup were in different subclusters and, conversely, nine subclusters included completely different serotypes. The closely relatedcpsloci within a subcluster were compared to the known CPS structures to relate gene content to structure. TheStreptococcus oralisandStreptococcus mitispolysaccharide biosynthetic loci clustered within the pneumococcalcpsloci and were in a subcluster that also included thecpslocus of pneumococcal serotype 21, whereas theStreptococcus agalactiae cpsloci formed a single cluster that was not closely related to any of the pneumococcalcpsclusters.