Bacterial viruses ("phages") play important roles in the regulation and evolution of microbial communities in most ecosystems. Terrestrial hot springs typically contain thermophilic bacterial communities, but the diversity and impacts of its associated viruses ("thermophilic phages") are largely unexplored. Here, we provide a taxonomic overview of phages that have been isolated strictly from terrestrial hot springs around the world. In addition, we placed 17 thermophilic phage genomes in a global phylogenomic context to detect evolutionary patterns. Thermophilic phages have diverse morphologies (e.g., tailed, filamentous), unique virion structures (e.g., extremely long tailed siphoviruses), and span five taxonomic families encompassing strictly thermophilic phage genera. Within the phage proteomic tree, six thermophilic phage-related clades were identified, with evident genomic relatedness between thermophilic phages and archaeal viruses. Moreover, whole proteome analyses showed clustering between phages that infect distinct host phyla, such as Firmicutes and Deinococcus-Thermus. The potential for discovery of novel phage-host systems in terrestrial hot springs remain mostly untapped, thus additional emphasis on thermophilic phages in ecological prospecting is encouraged to gain insights into the microbial population dynamics of these environments.
Keywords: Gammasphaerolipovirus; Hot spring; Thermophilic phage; Thermus; Viral metagenomics.