Prevalent chromosome fusion in Vibrio cholerae O1

Two circular chromosomes are a defining feature of the bacterial family Vibrionaceae, including the pathogen Vibrio cholerae, with rare reports of isolates with a single, fused chromosome. Here, we use long-read sequencing to analyse 467 V. cholerae O1 isolates from 47 cholera patients and household contacts in Bangladesh. We identify several independent chromosome fusion events that are likely transmissible within a household. Fusions occur in a 12 kilobase-pair homologous sequence shared between the two chromosomes and are stable for at least 200 generations under laboratory conditions. We find no detectable effect of fusion on V. cholerae growth, virulence factor expression, or biofilm formation. The factors promoting fusion, affecting chromosome stability, and subtle phenotypic or clinical consequences merit further investigation.