Metabarcoding approach for monitoring the fecal microbial diversity and pathogen reservoir role of Black tailed Gulls with a focus on Vibrio in South Korea

The increasing overlap between urban expansion and natural ecosystems requires a One Health perspective that integrates human, animal, and environmental health. Gulls of the genus Larus are closely associated with anthropogenic environments and may serve as reservoirs and vectors of microbial pathogens, yet their microbial ecology in Korea remains largely unexplored. To address this gap, we characterized the fecal microbiota of Black tailed Gulls,, a widespread seabird in East Asia, along the Incheon coast of Korea. A total of 75 fecal samples were analyzed from four sites using 16S rRNA gene metabarcoding. The gull microbiota was dominated by Firmicutes across all locations, with a shared core community, but also exhibited significant regional variation. The genus Cetobacterium was enriched in Yeonsu, Namdong, and Siheung, whereas Junggu was characterized by a high abundance of Lactobacillus and Streptococcus. Species-specific PCR further identified Vibrio parahaemolyticus, V. cholerae, and V. vulnificus in the samples. While major virulence genes were absent in V. cholerae and V. parahaemolyticus, all V. vulnificus isolates carried the vvp virulence gene, confirming their pathogenic potential. To our knowledge, this is the first metabarcoding-based investigation of gull-associated microbiota in Korea and the first to document the occurrence of Vibrio spp. in Black tailed Gulls in the region. These findings demonstrate that L. crassirostris harbors diverse microbial communities, including potential zoonotic pathogens, and may contribute to their dissemination across marine and urban interfaces. Integrating seabird surveillance into existing environmental and public health monitoring frameworks would strengthen Korea preparedness for pathogen transmission risks under a One Health approach.