Vibrio ‐bivalve interactions in health and disease

n the marine environment, bivalve mollusks constitute habitats for bacteria of the Vibrionaceae family. Vibrios belong to the microbiota of healthy oysters and mussels, which have the ability to concentrate bacteria in their tissues and body fluids, including the hemolymph. Remarkably, these important aquaculture species respond differently to infectious diseases. While oysters are the subject of recurrent mass mortalities at different life stages, mussels appear rather resistant to infections. Thus, Vibrio species are associated to the main diseases affecting the worldwide oyster production. Here we review the current knowledge on Vibrio‐bivalve interaction in oysters (Crassostrea sp.) and mussels (Mytilus sp.). We discuss the transient versus stable associations of vibrios with these bivalves as well as technical issues limiting the precise monitoring of vibrios in health and disease. Based on the current knowledge of oyster/mussel immunity and their interactions with Vibrio species pathogenic for oyster, we discuss how differences in immune effectors could contribute to the higher resistance of mussels to infections. Finally, we review the multiple strategies evolved by pathogenic vibrios to circumvent the potent immune defenses of bivalves and how key virulence mechanisms could have been positively or negatively selected in the marine environment through interactions with predators.