New publication in Cell Systems: Degradation of host translational machinery drives tRNA acquisition in viruses


Bacterial viruses (phage) are ubiquitous enemies of bacteria, able to efficiently infect and kill their hosts. Because phage rely on their host as a resource for reproduction, they are thought to be under strong selective pressure to maintain compact genomes and thus depend on host cell translational machinery for reproduction. However, some viruses encode abundant tRNA and other translation-related genes, which has been interpreted as an adaptation to differing codon usage between phage and host genomes. A fresh look at this old paradigm suggests that tRNA acquisition is driven by host DNA and RNA degrading upon infection, including host tRNAs, which are replaced by those of the phage. These tRNAs are expressed at levels slightly better adapted to phage codon usage, especially that of late genes. The phage is unlikely to randomly acquire as diverse an array of tRNAs as observed (p = 0.0017). Together, these results support that the main driver behind phage tRNA acquisition is pressure to sustain translation as host machinery degrades, a process resulting in a dynamically adapted codon usage strategy during the course of infection.