The ATP-binding cassette (ABC) transporter YbiT deficient mutant of Riemerella anatipestifer displays attenuation and confers promoting immune protection in geese.

Riemerella anatipestifer (RA) causes infectious serositis in poultry, leading to high mortality. ATP-binding cassette (ABC) transporters participate in diverse biological processes, but the role of the ABC transporter YbiT in RA remains unclear. Using the goose-derived RA strain CL-1 as the wild-type strain, we constructed a ybiT deletion mutant to investigate its biological functions and pathogenicity. Deletion of ybiT significantly impaired the growth of RA in TSB. Growth assays using DIP (2,2'-Dipyridyl) and various metal ions suggested a potential role for YbiT in Fe²⁺ transport. The mutant also exhibited reduced survival under acidic stress and displayed an elongated cellular morphology. Transcriptomic analysis revealed 427 differentially expressed genes (180 upregulated and 247 downregulated) in the mutant, indicating extensive transcriptional reprogramming. Animal infection assays demonstrated that the ΔybiT mutant was highly attenuated. Specifically, the LD₅₀ of the wild-type strain was 3 × 104 CFU, whereas no mortality was observed in geese challenged with up to 3.1 × 107 CFU of the mutant. In addition, geese infected with the mutant exhibited reduced bacterial loads and milder pathological lesions. Notably, a single immunization with as few as 104 CFU of the mutant conferred robust protection against subsequent wild-type challenge in goslings. Collectively, these findings identify ybiT as an important virulence-associated gene and establish the ΔybiT mutant as a promising live attenuated vaccine candidate.