Abstract
The arms race between bacteria and their bacteriophages profoundly influences microbial evolution. With an estimated 1023 phage infections occurring per second, there is strong selection for both bacterial survival and phage coevolution for continued propagation. Many phage resistance systems, including restriction-modification systems, clustered regularly interspaced short palindromic repeat-Cas (CRISPR-Cas) systems, a variety of abortive infection systems, and many others that are not yet mechanistically defined, have been described. Temperate bacteriophages are common and form stable lysogens that are immune to superinfection by the same or closely related phages. However, temperate phages collude with their hosts to confer defense against genomically distinct phages, to the mutual benefit of the bacterial host and the prophage. Prophage-mediated viral systems have been described in Mycobacterium phages and Pseudomonas phages but are predicted to be widespread throughout the microbial world. Here we describe a new viral defense system in which the mycobacteriophage Sbash prophage colludes with its Mycobacterium smegmatis host to confer highly specific defense against infection by the unrelated mycobacteriophage Crossroads. Sbash genes 30 and 31 are lysogenically expressed and are necessary and sufficient to confer defense against Crossroads but do not defend against any of the closely related phages grouped in subcluster L2. The mapping of Crossroads defense escape mutants shows that genes 132 and 141 are involved in recognition by the Sbash defense system and are proposed to activate a loss in membrane potential mediated by Sbash gp30 and gp31.IMPORTANCE Viral infection is an ongoing challenge to bacterial survival, and there is strong selection for development or acquisition of defense systems that promote survival when bacteria are attacked by bacteriophages. Temperate phages play central roles in these dynamics through lysogenic expression of genes that defend against phage attack, including those unrelated to the prophage. Few prophage-mediated viral defense systems have been characterized, but they are likely widespread both in phage genomes and in the prophages integrated in bacterial chromosomes.
Highlights
The arms race between bacteria and their bacteriophages profoundly influences microbial evolution
The microbial arms race between bacteriophage predators and bacterial prey has promoted evolution of a phage population that is genetically enormously diverse [1], with strong selection for bacterial acquisition of phage resistance mechanisms to defend against viral attack and the need for phage coevolution [2]
® mbio.asm.org 1 described [7,8,9], recent evidence suggests that temperate bacteriophages collude extensively with their bacterial hosts to provide defense against viral attack [10, 11]; these extend beyond well-known homotypic defenses such as repressor-mediated superinfection immunity to novel heterotypic defense systems, including some with exquisite specificity [11]
Summary
The arms race between bacteria and their bacteriophages profoundly influences microbial evolution. ® mbio.asm.org 1 described [7,8,9], recent evidence suggests that temperate bacteriophages collude extensively with their bacterial hosts to provide defense against viral attack [10, 11]; these extend beyond well-known homotypic defenses (i.e., against themselves) such as repressor-mediated superinfection immunity to novel heterotypic defense systems (i.e., against genomically different phages), including some with exquisite specificity [11]. Such prophage-mediated heterotypic defense systems may be widespread, but few have been described in detail or are mechanistically understood. These systems have been largely overlooked because of the dearth of well-defined collections of phages that infect common bacterial host strains
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
