Viral satellites exploit phage proteins to escape degradation of the bacterial host chromosome

Abstract

Phage defense systems are often found on mobile genetic elements (MGEs), where they constitutively defend against invaders or are induced to respond to new assaults. Some MGEs, the phage satellites, exploit phages for their own transmission after induction, reducing phage production and protecting their hosts in the process. One such satellite in Vibrio cholerae, PLE, is triggered by the lytic phage ICP1 to excise from the chromosome, replicate, and transduce to neighboring cells, completely sabotaging phage production. Here, we found that ICP1 has evolved to possess one of two syntenic loci encoding an SF1B-type helicase, either of which PLE can exploit to directly drive PLE replication. Further, loss of PLE mobilization limits anti-phage activity due to phage-mediated degradation of the bacterial genome. Our work provides insight into the unique challenges imposed on the parasites of lytic phages and underscores the adaptions of these satellites to their ever-evolving target phage.