Molecular organization of the genes required for the synthesis of type 1 capsular polysaccharide of Streptococcus pneumoniae: formation of binary encapsulated pneumococci and identification of cryptic dTDP‐rhamnose biosynthesis genes

Abstract

SummaryWe report here the molecular organization of the capsular locus (cap1 ) of the type 1 pneumococcus. This locus is located between dexB and aliA and flanked by IS1167 insertion elements. Sequence analysis showed that the cluster contains 11 genes (cap1A to cap1K ), which are apparently arranged as a single transcriptional unit. The presence of a functional promoter (cap1p ) located upstream of cap1A has been demonstrated and the transcription start point was mapped by primer-extension analysis. A 14.3 kb fragment containing the genes cap1ABCDEFGHIJK and including cap1p was sufficient to allow the synthesis of a type 1 capsule in Streptococcus pneumoniae. An internal deletion of cap1E leads to an unencapsulated phenotype demonstrating that this gene is essential for capsular production. The cap1K gene has been expressed in Escherichia coli resulting in UDP-glucose dehydrogenase (UDP-GlcDH) activity. Moreover, this gene was able to restore the synthesis of type 3 capsule when cloned into a plasmid and introduced by transformation into S. pneumoniae cap3A mutants deficient in UDP-GlcDH. In marked contrast with what was previously thought, recombination between cap1K and cap3A does occur. We provide data on the molecular mechanism that leads to the formation of binary encapsulated pneumococcal cells, i.e. strains that simultaneously produce type 1 and type 3 capsules.

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

“…In this study the role of transcription of the capsule operon was investigated. Since the capsule operon appears to be arranged as a single transcriptional unit (Morona et al, 1997;Munoz et al, 1997), transcription of the first gene of the capsule operon, cpsA, was measured. This study was limited to in vitro cpsA expression with quantification of capsule polysaccharide for only two isolates.…”

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).…”

Organization and characterization of the capsule biosynthesis locus of Streptococcus pneumoniae serotype 9V The GenBank accession number for the sequence reported in this paper is AF402095.

“…The genes are clustered within the chromosome and in all but one serotype (serotype 37) are located between dexB and aliA (Llull et al, 1999). At this time the CPS synthesis (cps) loci of 15 serotypes (1, 2, 3, 4, 6B, 8, 14, 18C, 19F, 19A, 19B, 19C, 23F, 33F and 37) have been sequenced (Arrecubieta et al, 1995 ;Dillard et al, 1995 ;Iannelli et al, 1999 ;Jiang et al, 2001 ;Kolkman et al, 1997b ;Llull et al, 1998Llull et al, , 1999Morona et al, 1997aMorona et al, , b, 1999aMunoz et al, 1997Munoz et al, , 1999. Sequence analysis and function predictions suggest that the loci contain the complete repertoire of genes specifically required for capsule biosynthesis and its regulation.…”

“…Sequence analysis and function predictions suggest that the loci contain the complete repertoire of genes specifically required for capsule biosynthesis and its regulation. In a few cases, the function of a gene has been experimentally confirmed (Arrecubieta et al, 1995(Arrecubieta et al, , 1996Kolkman et al, 1996Kolkman et al, , 1997aMorona et al, 1997aMorona et al, , 2000Munoz et al, 1997). Knowledge of the composition of the various cps loci and the function of the encoded proteins is important as it provides insight into the dynamics of the capsule biosynthesis pathway and the evolution of serotypes.…”