DNA-DNA homology between plasmids from Streptococcus thermophilus

Abstract - Fifty strains of Streptococcus thermophilus isolated from raw milk, industrial starters or issued from collections were studied for their plasmid complement. Most of them did not contain plasmid DNA. Six strains only harboured one plasmid and three strains two plasmids. All these plasmids were small sized: 2.9 to 7.6 kilobases. Restriction analysis and DNA-DNA hybridization were used to demonstrate similarity between plasmids of these strains and to distinguish several homology groups among them.

Résumé - Homologie de l'ADN des plasmides de Streptococcus thermophilus
Nous avons étudié le contenu plasmidique de cinquante souches de Streptococcus thermophilus isolées de laits crus, de ferments industriels ou issues de collection. La plupart d'entre elles ne contiennent pas de plasmides. Six souches possèdent un seul plasmide et trois souches possèdent deux plasmides. Tous ces plasmides sont de petite taille : de 2,9 à 7,6 kilobases. L'analyse de restriction et l'hybridation ADN-ADN ont permis de montrer des similitudes entre les plasmides de ces souches et de distinguer plusieurs groupes d'homologie parmi eux.