Contents lists available at ScienceDirect Fish and Shellfsh Immunology journal homepage: www.elsevier.com/locate/fsi Full length article Responsesof Mytilus galloprovincialis tochallengewiththeemergingmarine pathogen Vibrio coralliilyticus Teresa Balbi a,∗ , Manon Auguste a , Katia Cortese b , Michele Montagna a , Alessio Borello a , Carla Pruzzo a , Luigi Vezzulli a ,LauraCanesi a a Dept. of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Italy b Dept. of Experimental Medicine (DIMES), University of Genoa, Italy ARTICLEINFO Keywords: Bivalves Pathogenic vibrios Vibrio coralliilyticus Mediterranean mussels Hemocytes Immune response Embryos ABSTRACT Vibrio coralliilyticus has emerged as a coral pathogen of concern throughout the Indo-Pacifc reef. The interest towardsunderstandingitsecologyandpathogenicpotentialhasincreasedsince V. coralliilyticus wasshowntobe stronglyvirulentalsoforotherspecies;inparticular,itrepresentsaseriousthreatforbivalveaquaculture,being one of the most important emerging pathogen responsible for oyster larval mortalities worldwide. V. cor- alliilyticus has a tightly regulated temperature-dependent virulence and it has been related to mass mortalities events of benthic invertebrates also in the temperate northwestern Mediterranean Sea. However, no data are availableontheefectsof V. coralliilyticus inthemussel Mytilus galloprovincialis,themostabundantaquacultured speciesinthisarea.Inthiswork,responsesof M. galloprovincialis tochallengewith V. coralliilyticus (ATCCBAA- 450)wereinvestigated.Invitro,shorttermresponsesofmusselhemocyteswereevaluatedintermsoflysosomal membrane stability, bactericidal activity, lysozyme release, ROS and NO production, and ultrastructural changes, evaluated by TEM. In vivo, hemolymph parameters were measured in mussels challenged with V. coralliilyticus at24hp.i.Moreover,theefectsof V. coralliilyticus onmusselearlyembryodevelopment(at48hpf) were evaluated. The results show that both in vitro and in vivo, mussels were unable to activate immune re- sponsetowards V. coralliilyticus,andthatchallengemainlyinducedlysosomalstressinthehemocytes.Moreover, V. coralliilyticus showedastrongandconcentration-dependentembryotoxicity.Overall,theresultsindicatethat, although M. galloprovincialis is considered a resistant species to vibrio infections, the emerging pathogen V. coralliilyticus can represent a potential threat to mussel aquaculture. 1. Introduction Marine bivalves, due to their flter-feeding habit, accumulate large numbers of bacteria from the harvesting waters. Bivalves possess both cellular and humoral defence mechanisms that co-operate to kill and eliminate infecting bacteria [1,2]. However, some bacteria can be pa- thogenictothebivalvehost,inparticularthosebelongingtothegenus Vibrio. Pathogenic vibrios can mainly afect larval stages of cultured bivalves,andarealsoinvolvedindiseasesofjuvenilesandadults[3–5]. The Vibrio species with importance for bivalve hatcheries due to the known pathogenicity for larvae and spat have been recently summar- ized [6]. These include species from the Anguillarum, Coralliilyticus, Harveyi, Orientalis, Pectenicida and Splendidus clades. Vibrio coralliilyticus has emerged as a coral pathogen of concern throughout the Indo-Pacifc reef[7,8]. The interest towards under- standing its ecology and pathogenic potential has increased since V. coralliilyticus was shown to be strongly virulent also for other species, such as unicellular algae [9,10], fies [10,11], rainbow trout (Oncor- hynchus mykiss)andlarvalbrineshrimp(Artemia spp.)[12].Moreover, V. coralliilyticus represents a serious threat for bivalve aquaculture, being one of the most important emerging pathogen responsible for oyster larval mortalities worldwide [13–15]. V. coralliilyticus has been also associated with outbreaks of vibriosis in several other bivalve species,suchashardclam(Mercenaria mercenaria),NewZealandgreen- lipped mussel (Perna canaliculus), Atlantic bay scallop (Argopecten ir- radians) and naval shipworm (Teredo navalis)[13,15]. In the purple gorgonian Paramuricea clavata of the temperate north-western Medi- terranean Sea, experimental infections with V. coralliilyticus showed a tightly regulated temperature-dependent virulence, in a range of tem- peratures consistent with those observed during the occurrence of mortality episodes in the feld [16]. However, no information is avail- able of the efects of V. coralliilyticus in the Mediterranean mussel https://doi.org/10.1016/j.fsi.2018.10.011 Received21June2018;Receivedinrevisedform2October2018;Accepted5October2018 ∗ Corresponding author. Dept. of Earth, Environment and Life Sciences (DISTAV), University of Genoa, Corso Europa, 26 16132, Genoa, Italy. E-mail address: Teresa.Balbi@unige.it (T. Balbi). Fish and Shellfish Immunology 84 (2019) 352–360 Available online 06 October 2018 1050-4648/ © 2018 Elsevier Ltd. All rights reserved. T