| The type 2 capsule locus of Streptococcus pneumoniae is comprised of 17 open reading frames (ORFs) whose genes are presumed to be transcribed as an operon. Four genes, cpsA, cpsB, cpsC, and cpsD, comprise the upstream common genes. Based on sequence homology, CpsA may play a role in the regulation of capsule expression. CpsA has three hydrophobic segments at its N terminus. Using Western analyses, we have shown that CpsA localizes to the cell membrane of fractionated cells from the type 2 parent strain. An internal deletion of cpsA was constructed in the type 2 parent strain D39. The cps2A deletion mutants were capable of producing polymer; however, electron microscopy revealed a sparse and uneven distribution of capsule on the surface. Increased binding of type 2 polyclonal antisera, antibody to complement opsonized bacteria, and antibody to non-capsular antigens such as phosphocholine was observed. Transcriptional analyses using cat fusions in the parent and cps2A deletion mutants showed no difference in promoter activity when resistance levels to chloramphenicol were measured. Mutants in Cps2A were significantly reduced in virulence when mice were infected by intravenous (i.v.) and intraperitoneal (i.p.) routes. They were also unable to colonize the nasopharynx.;In addition to capsule alterations, the cps2A deletion mutants also exhibited a loss of beta-galactosidase activity due to a significant reduction in transcription of bgaA, which is the gene encoding beta-galactosidase. These differences were not attributed exclusively to mutation of cps2A, however, as derivatives containing mutations in other common genes also had reduced beta-galactosidase activity. In S. pneumoniae , beta-galactosidase, BgaA, is associated with the cell surface. Mutations in bgaA caused an increase in capsule production but did not affect virulence or nasopharyngeal colonization of mice. Regulation of bgaA due to alterations in capsule production suggests a complex regulatory network which possibly is under the control of capsule common genes. Characterization of co-regulated factors due to alterations in capsule production could help to understand the disease processes of S. pneumoniae. |
