Responses of Mytilus galloprovincialis to challenge with environmental isolates of the potential emerging pathogen Malaciobacter marinus

• Published in: Fish & Shellfish Immunology
• Main Authors: Auguste, Manon, Rahman, Faiz Ur, Balbi, Teresa, Leonessi, Martina, Oliveri, Caterina, Bellese, Grazia, Vezzulli, Luigi, Furones, Dolors, Canesi, Laura
• Other Authors: Furones, Dolor
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: Bivalve; Hemocyte; Immune response; LC3; Larvae; Malaciobacter marinu; Mussel; mTor; Crassostrea gigas
• Online Access: http://hdl.handle.net/11567/1098213; https://doi.org/10.1016/j.fsi.2022.09.048

Bacteria of the Arcobacter-like spp. represent emerging foodborne zoonotic pathogens in humans and animals. Their increasing presence in seafood, suggesting higher occurrence in seawater due to marine pollution, is raising some environmental concern. Although Arcobacter is frequently detected in diseased oysters and stressed bivalve species, no data are available so far on its potential pathogenicity or interactions with the immune system of the bivalve host. In this work, responses to challenge with two strains of Malaciobacter marinus IRTA-19-131 and IRTA-19-132, R1 and R2), isolated from adult Crassostrea gigas during a mortality event in 2019 in Spain, were investigated in the mussel Mytilus galloprovincialis. In vivo experiments were performed in larvae (48h post-fertilization), and in adult mussels at 24h post-injection, in order to evaluate the pathogenicity for early developmental stages, and the hemolymph immune responses, respectively. Both R1 and R2 were moderately pathogenic to early larvae, with significant decreases in the development of normal D-veligers from 104 and 103CFU/mL, respectively. In adults, both strains decreased hemocyte lysosomal membrane stability (LMS), and stimulated extracellular defense responses (ROS production and lysozyme activity). The interactions between mussel hemocytes and M. marinus were investigated in in vitro short-term experiments (30-90min) using the R1 strain (106-108CFU/mL). R1 decreased LMS and induced lysosomal enlargement, but not cell detachment or death, and stimulated extracellular ROS production and lysozyme release, confirming in vivo data. Moreover, lysosomal internalization and degradation of bacteria were observed, together with changes in levels of activated mTor and LC3, indicating phagocytic activity. Overall, the results indicate the activation of both extracellular and intracellular immune defenses against M. marinus R1. Accordingly, these responses resulted in a significant hemolymph bactericidal activity, with a large contribution of hemolymph ...