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Type 1 Capsule Genes of Staphylococcus aureus Are Carried in a Staphylococcal Cassette Chromosome Genetic Element. Thanh T. Luong, 2002.The cap1 genes are required for the synthesis of type 1 capsular polysaccharide (CP1) in Staphylococcus aureus . We previously showed that the cap1 locus was associated with a discrete genetic element in S . aureus M . In this report, we defined the boundaries of the cap1 element by comparing its restriction pattern to that of a corresponding region from the CP1-negative strain Becker . The element was located in the SmaI-G chromosomal fragment of the standard mapping strain NCTC8325 . The sequences of the entire cap1 element and the flanking regions were determined . We found that there were two additional cap1 genes not previously identified . The cap1 operon was located in a staphylococcal cassette chromosome (SCC) element similar to the resistance island SCCmec recently described for methicillin resistance in S . aureus . Notably, the SCCcap1 element was located at the same insertion site as all the SCCmec elements in the staphylococcal chromosome . The excision of SCCcap1 could be demonstrated only in the presence of the recombinase genes from an SCCmec element, verifying that SCCcap1 is a genuine SCC element but defective in mobilization . A novel enterotoxin gene, whose transcript was detected by Northern blotting, was found next to the SCCcap1 locus . We propose that the enterotoxin gene and SCCcap1 were inserted into this locus at the juxtaposition by independent events . Sequence comparison revealed numerous DNA rearrangements and mutations in SCCcap1 and the left flanking region, suggesting that the SCCcap1 had been inserted at the SCC attC site a long time ago . In addition, most genes in this region were incomplete, with the exception of the 15 cap1 genes, implying that the cap1 genes confer a survival advantage on strain M . Analysis of the Corynebacterium diphtheriae DtxR Regulon: Identification of a Putative Siderophore Synthesis and Transport System That Is Similar to the Yersinia High-Pathogenicity Island-Encoded Yersiniabactin Synthesis and Uptake System. Carey A. Kunkle, 2003.The diphtheria toxin repressor, DtxR, is a global iron-dependent regulatory protein in Corynebacterium diphtheriae that controls gene expression by binding to 19-bp operator sequences . To further define the DtxR regulon in C . diphtheriae, a DtxR repressor titration assay (DRTA) was developed and used to identify 10 previously unknown DtxR binding sites . Open reading frames downstream from seven of the newly identified DtxR binding sites are predicted to encode proteins associated with iron or heme transport . Electrophoretic mobility shift assays indicated that DtxR was able to bind to DNA fragments carrying the 19-bp operator regions, and transcriptional analysis of putative promoter elements adjacent to the binding site sequences revealed that most of these regions displayed iron- and DtxR-regulated activity . A putative siderophore biosynthesis and transport operon located downstream from one of the DtxR binding sites, designated sid, is similar to the yersiniabactin synthesis and uptake genes encoded on the Yersinia pestis high pathogenicity island . The siderophore biosynthetic genes in the sid operon contained a large deletion in the C . diphtheriae C7 strain, but the sid genes were unaffected in four clinical isolates that are representative of the dominant strains from the recent diphtheria epidemic in the former Soviet Union . Mutations in the siderophore biosynthetic genes in a clinical strain had no effect on siderophore synthesis or growth in low-iron conditions; however, a mutation in one of the putative transport proteins, cdtP, resulted in reduced growth in iron-depleted media, which suggests that this system may have a role in iron uptake . The findings from this study indicate that C . diphtheriae contains at least 18 DtxR binding sites and that DtxR may affect the expression of as many as 40 genes .
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