Beyond Cholera: Characterization of zot-Encoding Filamentous Phages in the Marine Fish Pathogen Vibrio anguillarum

Zonula occludens toxin (Zot) is a conserved protein in filamentous vibriophages and has been reported as a putative toxin in Vibrio cholerae. Recently, widespread distribution of zot-encoding prophages was found among marine Vibrio species, including environmental isolates. However, little is known about the dynamics of these prophages beyond V. cholerae. In this study, we characterized and quantified the zot-encoding filamentous phage VAIϕ, spontaneously induced from the fish pathogen V. anguillarum. VAIϕ contained 6117 bp encoding 11 ORFs, including ORF8(pVAI), exhibiting 27%–73% amino acid identity to Inovirus Zot-like proteins. A qPCR method revealed an average of four VAIϕ genomes per host genome during host exponential growth phase, and PCR demonstrated dissemination of induced VAIϕ to other V. anguillarum strains through re-integration in non-lysogens. VAIϕ integrated into both chromosomes of V. anguillarum by recombination, causing changes in a putative ORF in the phage genome. Phylogenetic analysis of the V. anguillarum Inoviridae elements revealed mosaic genome structures related to mainly V. cholerae. Altogether, this study contributes to the understanding of Inovirus infection dynamics and mobilization of zot-like genes beyond human pathogenic vibrios, and discusses their potential role in the evolution of the fish pathogen V. anguillarum.