Degradation of host translational machinery drives tRNA acquisition in viruses

Viruses are traditionally thought to be under 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, potentially optimizing for codon usage differences between phage and host. Here, we systematically interrogate selective advantages that carrying 18 tRNAs may convey to a T4-like Vibriophage. Host DNA and RNA degrade 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, our 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. [Display omitted] •We ask what selective pressures drive tRNA carriage in a T4-like Vibriophage•Phage tRNAs are expressed at levels adapted to phage codon usage in late genes•Random acquisition of the diverse array of 18 phage tRNAs observed is unlikely•The phage has a dynamically adapted codon usage strategy Yang et al. systematically interrogate selective advantages that carrying 18 tRNAs may convey to a T4-like Vibriophage and find that the main driver behind phage tRNA acquisition is the pressure to sustain translation as host machinery degrades, a process resulting in a dynamically adapted codon usage strategy during the infection course.