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J. Bacteriol. doi:10.1128/JB.01058-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Extent of Horizontal Gene Transfer in Evolution of Streptococci of the Salivarius Group

Laboratoire de Génétique Microbienne, Institut National de Recherche Agronomique, 78352 Jouy-en-Josas Cedex, France., INSERM E44, Institut Cochin, Centre National de Référence des Streptocoques, Service de Bactériologie Hôpital Cochin, Faculté de Médecine Paris 5, 27 rue du faubourg Saint Jacques, 75679 Paris Cedex 14, France

^* To whom correspondence should be addressed. Email: christine.delorme{at}jouy.inra.fr,

	Abstract

The phylogenetically closely related species Streptococcus salivarius and Streptococcus vestibularis are oral bacteria considered as commensal, although they can be found also in human infections. The relationship between these two species, and between strains isolated from carriage or responsible of invasive infections has been investigated by multi locus sequence typing (MLST) and additional sequence analysis. Clustering of several S. vestibularis alleles and the extent of genomic divergence at certain loci support the status of S. salivarius and S. vestibularis as separate species. The sequence diversity in S. salivarius alleles is generally high whereas that of S. vestibularis is low at certain loci, indicating that the latter species might have evolved recently. Cluster analysis indicates occurrence of genetic exchange between S. salivarius and S. vestibularis at 3 out of the 9 investigated loci. Horizontal gene transfer between streptococci of the S. salivarius group and other oral streptococci was also detected at several loci. High level of recombination in S. salivarius was revealed by allele index association and split decomposition sequence analysis. Commensal and infection-associated S. salivarius strains could not be distinguished by clustering analysis, suggesting the opportunistic nature of the pathogen isolates. Taken together, our results point to a high level of gene exchange that contributes to the evolution of the two streptococcal species from the human oral cavity.

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