Killing of Vibrio cholerae and Escherichia coli Strains Carrying D-mannose-sensitive Ligands by Mytilus Hemocytes is Promoted by a Multifunctional Hemolymph Serum Protein

In aquatic environments, bivalve mollusks represent an important ecological niche for microorganisms. Persistence of bacteria in bivalve tissues partly depends on their capacity to survive the bactericidal activity of the hemolymph due to both cellular (hemocyes) and soluble serum factors (e.g., enzymes, lectins, opsonins). The extrapallial protein (EP) present in serum of Mytilus galloprovincialis (MgEP) has been recently shown to work as an opsonin promoting D-mannose sensitive (MS) interactions of the bivalve pathogen Vibrio aestuarianus 01/032 strain with the hemocytes. In this study, the role of MgEP in adhesion and killing of other bacteria carrying MS sensitive ligands was investigated. MgEP enhanced adhesion to and killing by hemocytes of Vibrio cholerae ElTor N16961, expressing the MS hemagglutin (MSHA), as well as of Escherichia coli MG1655, carrying type 1 fimbriae. These results further support the recent finding that the multifunctional MgEP also acts as an opsonin involved in mussel defense towards bacteria carrying MS ligands. In addition, these results contribute to elucidate the ecology of bacterial pathogens that can be transmitted to humans via shellfish consumption.