Pan-Genome Analysis of Vibrio cholerae and Vibrio metschnikovii Strains Isolated From Migratory Birds at Dali Nouer Lake in Chifeng, China

Abstract

Migratory birds are recently recognized as <i>Vibrio</i> disease vectors, but may be widespread transporters of <i>Vibrio</i> strains. We isolated <i>Vibrio cholerae (V. cholerae)</i> and <i>Vibrio metschnikovii (V. metschnikovii)</i> strains from migratory bird epidemic samples from 2017 to 2018 and isolated <i>V. metschnikovii</i> from migratory bird feces in 2019 from bird samples taken from the Inner Mongolia autonomous region of China. To investigate the evolution of these two <i>Vibrio</i> species, we sequenced the genomes of 40 <i>V. cholerae</i> strains and 34 <i>V. metschnikovii</i> strains isolated from the bird samples and compared these genomes with reference strain genomes. The pan-genome of all <i>V. cholerae</i> and <i>V. metschnikovii</i> genomes was large, with strains exhibiting considerable individual differences. A total of 2,130 and 1,352 core genes were identified in the <i>V. cholerae</i> and <i>V. metschnikovii</i> genomes, respectively, while dispensable genes accounted for 16,180 and 9,178 of all genes for the two strains, respectively. All <i>V. cholerae</i> strains isolated from the migratory birds that encoded T6SS and <i>hlyA</i> were non-O1/O139 serotypes without the ability to produce CTX. These strains also lacked the ability to produce the TCP fimbriae nor the extracellular matrix protein RbmA and could not metabolize trimetlylamine oxide (TMAO). Thus, these characteristics render them unlikely to be pandemic-inducing strains. However, a <i>V. metschnikovii</i> isolate encoding the complete T6SS system was isolated for the first time. These data provide new molecular insights into the diversity of <i>V</i>. <i>cholerae</i> and <i>V. metschnikovii</i> isolates recovered from migratory birds.