Environmental Virulence of Vibrio (EN3VI)

Characterization of the virulence of the pathogenic for oyster Vibrio tasmaniensis LGP 32, induced by dinoflagellate Alexandrium pacificum (catenella)

Project leader: Jean-Luc Rolland
This aims of this project is to decipher the virulence mechanisms of the pathogen V. tasmaniensis LGP32 induced by the dinoflagellate A. pacificum (catenella). For several years episodic events of massive mortality of juvenile oysters have occurred in on the French coasts. Strains of vibrios of the clade Splendidus are found associated with these recurrent mortalities events. However, under experimental conditions in the laboratory, the infection of the oyster Crassostrea gigas by these vibrios does not directly induce mortality. These data suggest that there are other biotic or abiotic factors that contribute to the virulence of vibrios under natural conditions. Among these factors, the biotic interactions with microorganisms of the natural environment, absent in our experimental conditions, remain little explored. Different species of vibrios are known for their particular interactions with planktonic microorganisms. These interactions range from predation to the acquisition of nutrients essential for their growth. Among the species, micro-algae represent a source of potential nutrients useful or even necessary for their growth, especially during the decomposition of these algae at the time of decline of the microalgae bloom. If this sudden collapse of phytoplankton populations especially during periods of high abundance (spring bloom) has been attributed to viruses, the involvement of marine bacteria is also likely. Several studies have demonstrated algicidal effects of Vibrios spp. on micro-algae, some of which are toxic such as Skeletonema costatum, Heterosigma akashiwo, Chattonella marina, Gymnodinium catenatum and Alexandrium tamarense. In a previous project ALGOVIR, we have shown for the first time that the toxic microalgae A. pacificum, which produces recurrent blooms in the Thau lagoon, promotes growth and increases the virulence of the pathogenic Vibrio tasmaniensis LGP32. In the EN3VI project, we will try to characterize the unknown role of this biotic interaction, micro-algae / vibrio, in the regulation of the virulence of V. tasmaniensis LGP32 pathogen. For this (i) we will characterize in vitro the LGP32 virulence mechanisms regulated by its interactions with the algae A. pacificum taking care to place our experiments in conditions close to those encountered in the environment and (ii) we will study, in situ during bloom events of A. pacificum, the regulation of virulence factors of V. tasmaniensis LGP32 identified in vitro.
Partner 1 – Interactions Hôtes-Pathogènes-Environnements (IHPE, Université de Montpellier, CNRS, Ifremer, UPVD, Montpellier, France): Rolland Jean-Luc, Destoumieux-Garzon Delphine, Lagorce Arnaud, Haffner Philippe, Leroy Marc.
Partener 2 – MARine Biodiversity, Exploitation and Conservation (MARBEC, Université de Montpellier, CNRS, Ifremer, IRD, Montpellier, France). Laabir Mohamed, Masseret Estelle, Abadie Eric.
Partner 3 – Diversité Genome et Interactions Microorganismes Insectes (DGIMI, Université de Montpellier, INRA, Montpellier, France). Givaudan Alain, Lanois-Nouri Anne.
Partner 4 –  Plateforme de PCR quantitative Haut débit (qHPD, Université de Montpellier). Clair Philippe