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

Abstract

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.

Comparative 16SrDNA Gene-Based Microbiota Profiles of the Pacific Oyster (Crassostrea gigas) and the Mediterranean Mussel (Mytilus galloprovincialis) from a Shellfish Farm (Ligurian Sea, Italy)

“…This is in line with the lower susceptibility of mussels, with respect to oysters, to pathogenic Vibrio species also in relation to the presence in mussels of specific hemolymph soluble components (MgEP) that mediate adhesion, internalization and killing of V. aestuarianus by the hemocytes [18][19]33]. Overall, these results indicate that Vibrio might play a contrasting role in health and disease of different bivalve species.…”

“…For instance, settings of environmental conditions in depuration plants favoring hemolymph-mediated bacterial killing (e.g. increasing the production of serum opsonins) [19] and phage therapy [43] have been proposed. However, none of these practices has yet been tested and proved to be successful in real aquaculture depuration facilities.…”

“…In particular the extrapallial protein (EP) present in serum of M. carrying MS sensitive ligands with the hemocytes [19]. Presence/absence of this and/or similar pathways driving microbial-host interactions in the haemolymph and other bivalve tissues may significantly impact microbiome structure and, in turn, influence susceptibility/resistance to microbial diseases in these animals.…”

Shift in Immune Parameters After Repeated Exposure to Nanoplastics in the Marine Bivalve Mytilus

“…This protein has been shown to play a key role in specific recognition of both selected bacterial strains and NP types. EPp promotes mannosesensitive interactions between Mytilus hemocytes and different bacterial strains of V. aestuarianus and Vibrio cholerae expressing mannose-sensitive hemagglutinin (MSHA) and Escherichia coli MG1655, carrying type 1 fimbriae, leading to activation of the immune response (34,45). Moreover, EPp represents the unique protein component of the stable biomolecular corona formed around PS-NH 2 in mussel hemolymph serum, which mediates specific recognition of this NP type by hemocytes and consequent immune response in vitro (18,46).…”

Biotechnologies from Marine Bivalves

“…Other molluscan lectins with biotechnological potential are two C-type lectins from C. gigas (CgCLec-4, CgCLec-5), which exhibited anti-microbial (agglutinating) activity against bacteria and fungi (Jia et al 2016). One extrapallial protein (C1Q-domain containing protein) of the mussel hemolymph serum (MgEP) was also demonstrated to act as an opsonin and to promote interactions between a suspected Vibrio pathogen and Mytilus hemocytes (Canesi et al 2016).…”