Novel Escherichia coli phages representing a distinct genus within the subfamily Stephanstirmvirinae: genome and host range characteristics.

Bacteriophages play crucial roles in microbial ecosystems and have potential for biotechnological applications. However, our understanding of culturable phages remains limited. In this study, we characterized six novel Escherichia coli phages isolated from pig farm wastewater and urban sewage, using comprehensive genomic, morphological, and host-range analysis. Using multiple comparative approaches, including gene-sharing network analysis, average nucleotide identity (ANI), and nucleotide intergenomic similarity (NIS), we demonstrated that five of these phages form a distinct group within the subfamily Stephanstirmvirinae, potentially representing a novel genus, for which we propose the name "Wecvirus". We further propose that these phages, each of which exhibits a unique host range pattern, should be classified in two distinct species within the proposed genus. This host specificity is reflected in differences in the amino acid sequences of tail fibers, which are crucial for infection. The remaining phage, which was not classified as a wecvirus, exhibited characteristics that challenged the current classification criteria, highlighting the need for more-flexible taxonomic approaches. These findings expand our understanding of phage diversity within the subfamily Stephanstirmvirinae and contribute to the evolving phage taxonomy framework.