Identification of a novel insertion sequence element in Streptococcus agalactiae

Gain and loss of bacterial pathogenicity is often associated with mobile ge netic elements. A novel insertion sequence (IS) element designated ISSa4 wa s identified in Streptococcus agalactiae (group B streptococci). The 963 bp IS element is flanked by 25 bp perfect inverted repeats and led to the dup lication of a 9 bp target sequence at the insertion site. ISSa4 contains on e open reading frame coding for a putative transposase of 287 aa and exhibi ts closest similarities to insertion elements of the IS982 family which has previously not been identified in streptococci. Analysis of different S. a galactiae strains showed that the copy number of ISSa4 in S. agalactiae var ies significantly between strains. The S. agalactiae strain with the highes t copy number of ISSa4 was nonhemolytic and harbored one copy inserted in c ylB, which encodes the membrane-spanning domain of the putative hemolysin t ransporter (Spellerberg et al., 1999. Identification of genetic determinant s for the hemolytic activity of Streptococcus agalactiae by ISSI transposit ion. J. Bacteriol. 181, 3212-3219). Determination of the distribution of IS Sa4 in different S. agalactiae strains revealed that ISSa4 could be detecte d only in strains isolated after 1996, which might indicate a recent acquis ition of this novel insertion element by S. agalactiae. (C) 2000 Elsevier S cience B.V. All rights reserved.