A family of viral satellites manipulates invading virus gene expression and affects cholera toxin mobilization

Abstract

AbstractMany viruses possess temporally unfolding gene expression patterns aimed at subverting host defenses, commandeering host metabolism, and ultimately producing a large number of progeny virions. High throughput -omics tools, such as RNA-seq, have dramatically enhanced resolution of expression patterns during infection. Less studied have been viral satellites, mobile genomes that parasitize viruses and have far reaching effects on host-cell fitness. By performing RNA-seq on infection time courses, we have obtained the first time-resolved transcriptomes for bacteriophage satellites during lytic infection. Specifically, we have acquired transcriptomes for the lytic Vibrio cholerae phage ICP1 and all five known variants of ICP1’s parasite, the Phage Inducible Chromosomal Island-Like Elements (PLEs). PLEs rely on ICP1 for both DNA replication and mobilization, and abolish production of ICP1 progeny in infected cells. We investigated PLEs impact on ICP1 gene expression and found that PLEs did not broadly restrict or reduce ICP1 gene expression. A major exception occurred in ICP1’s capsid morphogenesis operon, which was downregulated by each of the PLE variants. This transcriptional manipulation, conserved among PLEs, has also evolved independently in at least one other phage satellite, suggesting that viral satellites may be under strong selective pressure to reduce the capsid expression of their larger host viruses. Surprisingly, PLEs were also found to alter the gene expression of CTXϕ, the integrative phage that encodes cholera toxin and is necessary for virulence of toxigenic V. cholerae. One PLE, PLE1, upregulated CTXϕ genes involved in replication and integration, and boosted CTXϕ mobility following induction of the SOS response. Our data show that PLEs exhibit conserved manipulation of their host-phage’s gene expression, but divergent effects on CTXϕ, revealing that PLEs can influence both their hosts’ resistance to phage and the mobility of virulence encoding elements.