title: The diversity-generating benefits of a prokaryotic adaptive immune system.
abstract: Prokaryotic CRISPR-Cas adaptive immune systems insert spacers derived from viruses and other parasitic DNA elements into CRISPR loci to provide sequence-specific immunity. This frequently results in high within-population spacer diversity, but it is unclear if and why this is important. Here we show that, as a result of this spacer diversity, viruses can no longer evolve to overcome CRISPR-Cas by point mutation, which results in rapid virus extinction. This effect arises from synergy between spacer diversity and the high specificity of infection, which greatly increases overall population resistance. We propose that the resulting short-lived nature of CRISPR-dependent bacteria-virus coevolution has provided strong selection for the evolution of sophisticated virus-encoded anti-CRISPR mechanisms.
authors.affiliation: ESI and CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Stineke
authors.initials: S
authors.lastname: van Houte
authors.affiliation: ESI and CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Alice K E
authors.initials: AK
authors.lastname: Ekroth
authors.affiliation: ESI and CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Jenny M
authors.initials: JM
authors.lastname: Broniewski
authors.affiliation: ESI and CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.|CEFE UMR 5175, CNRS-Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, 1919, route de Mende 34293, Montpellier Cedex 5, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Chabas
authors.affiliation: Department of Integrative Biology, University of California, Berkeley, California 94720, USA.|CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Ben
authors.initials: B
authors.lastname: Ashby
authors.affiliation: Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California 94158, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Bondy-Denomy
authors.affiliation: CEFE UMR 5175, CNRS-Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, 1919, route de Mende 34293, Montpellier Cedex 5, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Gandon
authors.affiliation: Department of Integrative Biology, University of California, Berkeley, California 94720, USA.|CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Boots
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Paterson
authors.affiliation: ESI and CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Angus
authors.initials: A
authors.lastname: Buckling
authors.affiliation: ESI and CEC, Biosciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK.
authors.forename: Edze R
authors.initials: ER
authors.lastname: Westra
mesh_terms: D001435:Bacteriophages / Q000235:genetics / Q000276:immunology / Q000502:physiology; D005075:Biological Evolution; D064113:CRISPR-Cas Systems / Q000235:genetics* / Q000276:immunology*; D053476:Extinction, Biological; D056084:Genetic Fitness / Q000235:genetics / Q000502:physiology; D017354:Point Mutation / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000276:immunology* / Q000821:virology