Molecular Characterization ofStreptococcus pneumoniaeType 4, 6B, 8, and 18C Capsular Polysaccharide Gene Clusters

Abstract

Capsular polysaccharide (CPS) is a major virulence factor in Streptococcus pneumoniae. CPS gene clusters of S. pneumoniae types 4, 6B, 8, and 18C were sequenced and compared with those of CPS types 1, 2, 14, 19F, 19A, 23F, and 33F. All have the same four genes at the 5 end, encoding proteins thought to be involved in regulation and export. Sequences of these genes can be divided into two classes, and evidence of recombination between them was observed. Next is the gene encoding the transferase for the first step in the synthesis of CPS. The predicted amino acid sequences of these first sugar transferases have multiple transmembrane segments, a feature lacking in other transferases. Sugar pathway genes are located at the 3 end of the gene cluster. Comparison of the four dTDP-L-rhamnose pathway genes (rml genes) of CPS types 1, 2, 6B, 18C, 19F, 19A, and 23F shows that they have the same gene order and are highly conserved. There is a gradient in the nature of the variation of rml genes, the average pairwise difference for those close to the central region being higher than that for those close to the end of the gene cluster and, again, recombination sites can be observed in these genes. This is similar to the situation we observed for rml genes of O-antigen gene clusters of Salmonella enterica. Our data indicate that the conserved first four genes at the 5 ends and the relatively conserved rml genes at the 3 ends of the CPS gene clusters were sites for recombination events involved in forming new forms of CPS. We have also identified wzx and wzy genes for all sequenced CPS gene clusters by use of motifs.Streptococcus pneumoniae is an important human pathogen causing invasive diseases such as pneumonia, bacteremia, and meningitis. Control of pneumococcal diseases is being complicated by the increasing prevalence of antibiotic-resistant strains and the suboptimal clinical efficacy of existing vaccines. The capsular polysaccharide (CPS) of S. pneumoniae is essential for virulence because it protects S. pneumoniae from the nonspecific defence system of the host organism. All fresh isolates from patients with pneumococcal infection are encapsulated, and spontaneous nonencapsulated derivatives of such strains are almost completely avirulent (7).Ninety different CPS types have been identified so far by immunological and chemical techniques (31). Each has a structurally distinct CPS, composed of repeating oligosaccharide units joined by glycosidic linkages. CPS production requires a complex pathway, including synthesis of the activated monosaccharide nucleotide precursors, sequential transfer of each sugar to a lipid carrier to form repeating CPS units, and subsequent polymerization, export, and attachment to the cell surface. The exception to this is type 3 CPS, which has a very simple CPS structure and appears to be synthesized by a processive transferase (6). Classic genetic studies carried out by Austrian et al. (8) demonstrated that the genes encoding CPS biosynthesis are closely linked on the S. pneumoniae chromoso...

The variation of dTDP-l-rhamnose pathway genes in Vibrio cholerae

“…The situation for the Streptococcus pneumoniae CPS gene clusters is interesting in yet another way, because in this case the rml gene sets are located at the 39 end of the CPS gene clusters (Boulnois & Jann, 1989;Coffey et al, 1998;Jiang et al, 2001;Morona et al, 1997;Munoz et al, 1997).…”

“…pneumoniae CPS rml gene sets (Coffey et al, 1998;Jiang et al, 2001;Morona et al, 1997) revealed a gradient in the level of the variation among the genes. In this case the higher level of variation is at the 59 end of the rml gene sets, which for Strep.…”

In vitro expression of the first capsule gene of Streptococcus pneumoniae, cpsA, is associated with serotype-specific colonization prevalence and invasiveness

“…Capsule operons of different serotypes show a similar structure with some conservation, particularly within the first four genes, downstream of which are the serotype-specific genes (Garcia et al, 1999;Jiang et al, 2001;Bentley et al, 2006 conserved and may have a role in regulation of capsule expression (Guidolin et al, 1994).…”

Serotype Prediction for Frequently Isolated Serotypes of Streptococcus Pneumoniae by Heteroduplex Analysis and Modification of This Technique to Real-Time Fluorometric Nucleic Acid Detection System

“…The re sult of the se re com bi na ti ons is se roty pe switc hing among iso la tes wit hin ge ne tic li ne a ges. 14,15 In the re gi on bet we en the 3'-end of cpsA and the 5'-end of cpsB, the re are si tes of he te ro ge ne ity among se rotypes. 15,16 The cpsA and cpsB ge nes are in vol ved in the pro ces sing, re gu la ti on and ex port of the cap sular poly sacc ha ri de, 17 but they are not di rectly invol ved in cap su lar bi osyn the sis.…”

“…14,15 In the re gi on bet we en the 3'-end of cpsA and the 5'-end of cpsB, the re are si tes of he te ro ge ne ity among se rotypes. 15,16 The cpsA and cpsB ge nes are in vol ved in the pro ces sing, re gu la ti on and ex port of the cap sular poly sacc ha ri de, 17 but they are not di rectly invol ved in cap su lar bi osyn the sis. On the ot her hand, the cpsA and cpsB ge nes are physi cally linked to the se roty pe-spe ci fic ge nes and thus polymorp hism wit hin them wo uld be ex pec ted to be tightly lin ked to cap su lar type.…”