Isolation of novel phages from a resistant Dorea longicatena strain reveals genes associated with phage resistance.

The gut bacterium Dorea longicatena has been reported to be closely associated with metabolic disorders and has emerged as a promising target for microbiome interventions aiming at improving metabolic diseases. While phages serve as effective tools for precise modulation of gut bacteria, phage resources against this and other obligate anaerobic gut bacteria remain extremely limited, hindering both therapeutic development and studies of phage-host interactions. To address this gap and the challenge of rapid resistance emergence, we performed sequential screening by first generating phage-resistant D. longicatena mutants using a previously reported set of D. longicatena phages and then using these resistant mutants as hosts to isolate additional phages from environmental samples. This approach yielded two novel lytic phages, CPB1657 and CPB1660, which remained active against 27 of the 30 tested D. longicatena strains, including the wild-type strain and resistant derivatives. Genomic characterization confirmed their lytic properties and absence of virulence or lysogeny genes. In addition, resistance to the initial phage was strongly associated with mutations in the major tail protein-like gene MAG_TPA_asm. Several mutants resistant to all tested phages shared an identical set of seven missense mutations in this gene. Together, these findings expand the currently limited phage resources available for D. longicatena and provide new insight into phage-host interactions in anaerobic gut bacteria.