Abstract

Type I CRISPR-Cas systems are abundant and widespread adaptive immune systems in bacteria and can greatly enhance bacterial survival in the face of phage infection. Upon phage infection, some CRISPR-Cas immune responses result in bacterial dormancy or slowed growth, which suggests the outcomes for infected cells may vary between systems. Here we demonstrate that type I CRISPR immunity of Pectobacterium atrosepticum leads to suppression of two unrelated virulent phages, ɸTE and ɸM1. Immunity results in an abortive infection response, where infected cells do not survive, but viral propagation is severely decreased, resulting in population protection due to the reduced phage epidemic. Our findings challenge the view of CRISPR-Cas as a system that protects the individual cell and supports growing evidence of abortive infection by some types of CRISPR-Cas systems.

Highlights

  • Type I CRISPR-Cas systems are abundant and widespread adaptive immune systems in bacteria and can greatly enhance bacterial survival in the face of phage infection

  • To determine what stage of phage reproduction was impeded, we investigated the effects of CRISPR-Cas on defined aspects of infection

  • CRISPR-Cas caused a decrease in the efficiency of centre of infection (ECOI) formation (Fig. 1c), meaning that for ɸTE, only 4 or 1% of infected cells released at least one infectious phage

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Summary

Introduction

Type I CRISPR-Cas systems are abundant and widespread adaptive immune systems in bacteria and can greatly enhance bacterial survival in the face of phage infection. Some CRISPR-Cas immune responses result in bacterial dormancy or slowed growth, which suggests the outcomes for infected cells may vary between systems. Recent studies revealed that at least some CRISPR-Cas variants, belonging to types VI and III, induce cell dormancy through collateral RNA cleavage following target recognition[9,10,11,12,13]. Type I immunity against some phages resulted in population decline[18]. It appears that immunity mediated by type I systems may lead to different outcomes for infected cells

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