A single regulatory gene is sufficient to alter V ibrio aestuarianus pathogenicity in oysters

• Published in: Environmental microbiology Vol. 17; no. 11; pp. 4189 - 4199
• Main Authors: Goudenège, David, Travers, Marie Agnès, Lemire, Astrid, Petton, Bruno, Haffner, Philippe, Labreuche, Yannick, Tourbiez, Delphine, Mangenot, Sophie, Calteau, Alexandra, Mazel, Didier, Nicolas, Jean Louis, Jacq, Annick, Le roux, Frédérique
• Format: Journal Article
• Language: English
• Published: 01.11.2015
• ISSN: 1462-2912; 1462-2920
• DOI: 10.1111/1462-2920.12699

Summary Oyster diseases caused by pathogenic vibrios pose a major challenge to the sustainability of oyster farming. In F rance, since 2012 a disease affecting specifically adult oysters has been associated with the presence of V ibrio aestuarianus. Here, by combining genome comparison, phylogenetic analyses and high‐throughput infections of strains isolated before or during the recent outbreaks, we show that virulent strains cluster into two V . aestuarianus lineages independently of the sampling dates. The bacterial lethal dose was not different between strains isolated before or after 2012. Hence, the emergence of a new highly virulent clonal strain is unlikely. Each lineage comprises nearly identical strains, the majority of them being virulent, suggesting that within these phylogenetically coherent virulent lineages a few strains have lost their pathogenicity. Comparative genomics allowed the identification of a single frameshift in a non‐virulent strain. This mutation affects the varS gene that codes for a signal transduction histidine‐protein kinase. Genetic analyses confirmed that varS is necessary for infection of oysters and for a secreted metalloprotease expression. For the first time in a V ibrio species, we show here that VarS is a key factor of pathogenicity.