Vibrio aestuarianus isolated from Crassostrea gigas mortality events
Since 2012, a disease affecting juvenile and adult oyster has been associated with the presence of Vibrio aestuarianus suggestingthe possible (re-) emergence of this organismas a pathogen. By combining genomes comparison, phylogenetic analysis and high throughput infection, we show that virulent strains are grouped into two V. aestuarianus lineages without correlation with the date of isolation. The bacterial lethal dose was not different between strains isolated before or during the recent outbreaks excluding the hypothesis of the emergence a new genotype.
Each lineage is comprised of nearly identical strains and the large majority of the strains are virulent, suggesting that the non-virulent strains lost their pathogenicity. Comparative genomics allowed the identification of different frameshifts specific to non-virulent strains. One of these mutations affects the varA gene that encodes for a signal transduction histidine-protein kinase. Genetic analyses confirmed that varA is necessary for infection of oysters and for the metalloprotease activity and has to be considered as one of V. aetuarianus’ virulence factors.
Other frameshifts specific to non-virulent strains will be now investigated, as the ecological significance of the two virulent lineages.
De Decker S., Normand J., Saulnier D., Pernet F., Castagnet S. & Boudry P. (2011) Responses of diploid and triploid Pacific oysters Crassostrea gigas to Vibrio infection in relation to their reproductive status. Journal of Invertebrate Pathology 106(2):179-191.
De Decker, S. & Saulnier D. (2011) Vibriosis induced by experimental cohabitation in Crassostrea gigas: Evidence of early infection and down-expression of immune-related genes. Fish and Shellfish Immunology 30:691-699.
Saulnier D., De Decker S., Haffner P. (2009). Real-time PCR assay for rapid detection and quantification of Vibrio aestuarianus in oyster and seawater: A useful tool for epidemiologic studies. Journal of Microbiological Methods 77, 191-197.
Le Roux F., Zouine M., Chakroun N., Binesse J., Saulnier D., Bouchier C., Zidane N., Ma L., Rusniok C., Lajus A., Buchrieser C., Médigue C., Polz M., Mazel D. (2009). Genome sequence of Vibrio splendidus: an abundant planctonic marine species with a large genotypic diversity. Environmental Microbiology 11(8), 1959–1970.
Binesse J., Delsert C., Saulnier D., Champomier-Vergès M-C., Zagorec M., Munier- Le hmann H., Mazel D., Le Roux F. (2008). Mettaloprotease vsm is the major determinant of toxicity for extracellular products of Vibrio splendidus. Appl. Envir. Microbiol. 74: 7108-7117
Garnier M. Labreuche Y., Garcia C., Robert M., Nicolas J.L. (2007). Evidence for the Involvement of Pathogenic Bacteria in Summer Mortalities of the Pacific Oyster Crassostrea gigas. Microbial Ecology 53 (2), 187-196.
Le Roux F, Binesse J, Saulnier D, Mazel D. (2007). Construction of a Vibrio splendidus mutant lacking the metalloprotease gene vsm by use of a novel counterselectable suicide vector. Appl. Environ. Microbiol. 73: 777-784