Construction and evaluation of a chromosomal expression platform (CEP) for ectopic, maltose-driven gene expression in Streptococcus pneumoniae

Abstract
In this paper, the construction and evaluation of a chromosomal expression platform (CEP), which allows controlled gene expression following ectopic integration into the chromosome ofStreptococcus pneumoniae, is described. CEP is based on the well-studied maltosaccharide-inducible system. To facilitate integration at CEP, a plasmid, pCEP, capable of replication inEscherichia coli, but not inS. pneumoniae, was assembled. This plasmid contains an expression/selection cassette flanked on each side by more than 2 kb of pneumococcal DNA. The cassette comprises a maltose-inducible promoter, PM, separated from a kanamycin-resistance gene byNcoI andBamHI cloning sites. Clones harbouring the gene of interest integrated at CEP under the control of PMcan be obtained through direct transformation of anS. pneumoniaerecipient with ligation products between that gene andNcoI/BamHI-digested pCEP DNA, followed by selection for kanamycin-resistant transformants.

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