Jestvirus, a Novel Genus in the Family Autotranscriptaviridae Infecting Aeromonas.

Aeromonas species are ubiquitous, aquatic, opportunistic pathogens; however, their viral predators remain underexplored. Here, we isolated and characterized Aeromonas phage vB_AsaP_JS1, a dsDNA phage with a short non-contractile tail that infects Aeromonas salmonicida. Comparative analyses indicate that vB_AsaP_JS1 diverges from representative T7-like phages, with gene content similarity below 50% and a maximum amino acid identity of 70% or less. It forms a supported monophyletic clade in both phylogenomic and protein-based trees. Gene-sharing network analysis further shows that vB_AsaP_JS1 and its closest relatives form a distinct, isolated cluster, clearly separated from all currently recognized genera within the family Autotranscriptaviridae and related lineages of Caudoviricetes. Collectively, these features satisfy ICTV criteria for genus demarcation and support the establishment of a novel phage genus, tentatively designated Jestvirus. Functional annotation highlights a compact transcriptional module containing a single-subunit T7-like RNA polymerase and a streamlined replication packaging operon. Several putative host-interaction-related genes, including a deoxycytidine kinase homolog, a PelC-like protein, and a putative glycosidase, are encoded in the genome; their possible roles in nucleotide scavenging or host interaction during infection represent hypotheses that require experimental validation. Metagenomic read mapping reveals sequence-level signals related to vB_AsaP_JS1 in wastewater datasets from multiple geographic regions, suggesting a potentially wider environmental distribution for this phage lineage than previously recognized, though confirmation of phage identity and prevalence will require further investigation. Together, our results expand the known genomic diversity of T7-like phages and provide taxonomic, functional, and ecological evidence for a new phage lineage within Caudoviricetes.