Mike Tisza (@miketisza.bsky.social)

GuFi phages represent the most prevalent viral family-level clusters in the human gut microbiome Despite being important ecological modulators of the gut microbiome, bacteriophage diversity and function remain under-characterized. We show that short-read metagenomic surveys can miss even globally highly prevalent viral family-level clusters (VFCs), that can be readily assembled and characterized with long-read metagenomic data from a relatively small cohort (n=109). While gut Bacteroidota phages have been the prevailing focus in the literature, we show that highly prevalent gut phage families frequently have Firmicutes hosts (termed GuFi phages), with broad host ranges verified using proximity-ligation (Hi-C) sequencing data. High-throughput sequencing of virus-like particles from fecal samples detected frequent enrichment of GuFi phages across samples, revealing their under-appreciated impact on the gut microbiome. We report the first in vitro induction and imaging of members of prevalent GuFi clades including the candidate orders Heliusvirales , Astravirales (VFC 2) and Suryavirales (VFC 4). Our findings underscore the importance of GuFi phages with broad host ranges in the gut microbiome, and the utility of long-read sequencing for viral discovery, paving the way for deeper insights into the role of bacteriophages in human health and disease. ### Competing Interest Statement IL is an employee of Phase Genomics. National Medical Research Council, 23-0614 National Research Foundation, NRFI09-0015 A*STAR, C210812044 https://www.biorxiv.org/content/10.64898/2026.01.26.701711v1.full