Type 1 Capsule Genes of Staphylococcus aureus Are Carried in a Staphylococcal Cassette Chromosome Genetic Element

Abstract

ABSTRACT 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 Sma I-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 SCC mec recently described for methicillin resistance in S. aureus . Notably, the SCC cap1 element was located at the same insertion site as all the SCC mec elements in the staphylococcal chromosome. The excision of SCC cap1 could be demonstrated only in the presence of the recombinase genes from an SCC mec element, verifying that SCC cap1 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 SCC cap1 locus. We propose that the enterotoxin gene and SCC cap1 were inserted into this locus at the juxtaposition by independent events. Sequence comparison revealed numerous DNA rearrangements and mutations in SCC cap1 and the left flanking region, suggesting that the SCC cap1 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.