Changes of gill and hemocyte-related bio-indicators during long term maintenance of the vent mussel Bathymodiolus azoricus held in aquaria at atmospheric pressure.

The deep-sea hydrothermal vent mussel Bathymodiolus azoricus has been the subject of several studies aimed at understanding the physiological adaptations that vent animals have developed in order to cope with the particular physical and chemical conditions of hydrothermal environments. In spite of reports describing successful procedures to maintain vent mussels under laboratory conditions at atmospheric pressure, few studies have described the mussel's physiological state after a long period in aquaria. In the present study, we investigate changes in mucocytes and hemocytes in B. azoricus over the course of several months after deep-sea retrieval. The visualization of granules of mucopolysaccharide or glycoprotein was made possible through their inherent auto-fluorescent property and the Alcian blue-Periodic Acid Schiff staining method. The density and distribution of droplets of mucus-like granules was observed at the ventral end of lamellae during acclimatization period. The mucus-like granules were greatly reduced after 3 months and nearly absent after 6 months of aquarium conditions. Additionally, we examined the depletion of endosymbiont bacteria from gill tissues, which typically occurs within a few weeks in sea water under laboratory conditions. The physiological state of B. azoricus after 6 months of acclimatization was also examined by means of phagocytosis assays using hemocytes. Hemocytes from mussels held in aquaria up to 6 months were still capable of phagocytosis but to a lesser extent when compared to the number of ingested yeast particles per phagocytic hemocytes from freshly collected vent mussels. We suggest that the changes in gill mucopolysaccharides and hemocyte glycoproteins, the endosymbiont abundance in gill tissues and phagocytosis are useful health criteria to assess long term maintenance of B. azoricus in aquaria. Furthermore, the laboratory set up to which vent mussels were acclimatized is an applicable system to study physiological reactions such as hemocyte immunocompetence even in the absence of the high hydrostatic pressure found at deep-sea vent sites.

Deep sea immunity: unveiling immune constituents from the hydrothermal vent mussel Bathymodiolus azoricus.

Marine molluscs are subjected to constant microbial threats in their natural habitats. As a result, they represent suitable models for the study of the molecular mechanisms that govern defense reactions in marine organisms. To understand humoral and cellular defense reactions in animals defying extreme physical and chemical conditions we set out to investigate the deep sea hydrothermal vent mussel Bathymodiolus azoricus found in abundance at the Mid-Atlantic Ridge. In the present study, hemocytes were stimulated with compounds of microbial origin and cellular morphological alterations as well as the production of superoxide assessed. Consequently, zymosan, glucan and peptidoglycan were considered as potent inducers of cellular reactions for inducing drastic cell morphology changes and high levels of superoxide production. Furthermore, we have presented for the first time in a deep sea hydrothermal vent animal, molecular evidence of the Rel-homology domain, a conserved motif present in all members of the Rel/nuclear-factor NF-kappaB family. Additionally we have demonstrated the occurrence of the antibacterial gene mytilin in Bathymodiolus azoricus gill tissues. Our results support the premise of an evolutionary conserved innate immune system in Bathymodiolus. Such system is seemingly homologous to that of Insects and other Bivalves and may involve the participation of NF-kappaB transcription factors and antibacterial genes.