Publication :
Costs of CRISPR-cas-mediated resistance in Streptococcus thermophilus

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Date
2015-08-07
Auteurs
Vale, Pedro
Lafforgue, Guillaume
Gatchitch, François
Gardan, Rozenn
Gandon, Sylvain
Direction de publication
Direction de recherche
Titre de la revue
ISSN de la revue
Titre du volume
Éditeur
The Royal Society Publishing
Projets de recherche
Structures organisationnelles
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Résumé
CRISPR-Cas is a form of adaptive sequence-specific immunity in microbes. This system offers unique opportunities for the study of coevolution between bacteria and their viral pathogens, bacteriophages. A full understanding of the coevolutionary dynamics of CRISPR-Cas requires knowing the magnitude of the cost of resisting infection. Here, using the gram-positive bacterium Streptococcus thermophilus and its associated virulent phage 2972, a well-established model system harbouring at least two type II functional CRISPR-Cas systems, we obtained different fitness measures based on growth assays in isolation or in pairwise competition.We measured the fitness cost associated with different components of this adaptive immune system: the cost of Cas protein expression, the constitutive cost of increasing immune memory through additional spacers, and the conditional costs of immunity during phage exposure. We found that Cas protein expression is particularly costly, as Cas-deficient mutants achieved higher competitive abilities than the wild-type strain with functional Cas proteins. Increasing immune memory by acquiring up to four phage-derived spacers was not associated with fitness costs. In addition, the activation of the CRISPR-Cas system during phage exposure induces significant but small fitness costs. Together these results suggest that the costs of the CRISPR-Cas system arise mainly due to the maintenance of the defence system. We discuss the implications of these results for the evolution of CRISPR-Cas-mediated immunity.
Description
Revue
Proceedings of The Royal Society. Biological Sciences. Series B, Vol. 282 (1812), 1-9 (2015)
DOI
10.1098/rspb.2015.1270
URL vers la version publiée
Mots-clés
CRISPR , Immunity , Fitness costs
Citation
Type de document
article de recherche