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The type 2 capsule locus of Streptococcus pneumoniae
F Iannelli1, B J Pearce, G Pozzi
1Sezione di Microbiologia, Dipartimento di Biologia Molecolare, Università di Siena, 53100 Siena, Italy.
Abstract:
The type 2 capsule locus of Streptococcus pneumoniae was characterized in Avery's strain D39, which is the parent strain of the standard transformation recipients currently used in pneumococcal research and is largely used as a virulent strain in studies on the pathogenesis of pneumococcal infections. The capsule locus was sequenced by using a 21.7-kb PCR fragment from the D39 genome as a template. Sequence data analysis showed the presence of 18 open reading frames, 17 of which have the same direction of transcription and all of which are potentially involved in capsule biosynthesis. It was also shown that R36A and R6, which are unencapsulated (rough) derivatives of D39, carry a 7,504-bp deletion involving nine capsule genes.
Insights
The Streptococcus pneumoniae type 2 capsule locus in the virulent D39 strain was sequenced, revealing 18 genes potentially involved in capsule biosynthesis. Unencapsulated derivatives showed significant gene deletions.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Streptococcus pneumoniae is a significant human pathogen.
- Capsular polysaccharides are crucial virulence factors in S. pneumoniae.
- Strain D39 is a widely used virulent strain and parent for research recipients.
Purpose of the Study:
- To characterize the type 2 capsule locus of Streptococcus pneumoniae strain D39.
- To identify genes involved in capsule biosynthesis.
- To compare the capsule locus in virulent and unencapsulated strains.
Main Methods:
- Genomic DNA from strain D39 was used as a template for PCR amplification.
- A 21.7-kb PCR fragment containing the capsule locus was sequenced.
- Sequence data was analyzed to identify open reading frames (ORFs) and potential gene functions.
Main Results:
- The type 2 capsule locus of strain D39 comprises 18 open reading frames.
- Seventeen of these ORFs share the same transcriptional direction and are potentially involved in capsule biosynthesis.
- Unencapsulated derivatives (R36A and R6) possess a 7,504-bp deletion, encompassing nine capsule genes.
Conclusions:
- The characterized capsule locus provides a genetic basis for type 2 capsule production in S. pneumoniae D39.
- The identified genes are likely essential for capsule biosynthesis.
- Deletions in the capsule locus explain the unencapsulated phenotype of R36A and R6 strains.