Out of the deep sea into a land-based aquarium environment: investigating physiological adaptations in the hydrothermal vent mussel Bathymodiolus azoricus

Deep-sea hydrothermal vents are considered to be some of the most extreme environments in the world, yet the animals dwelling around the vent sites exhibit high productivity and must therefore deal with unusual levels of heavy metals, pH, temperature, CO2, and sulphides, in addition to environmental microbes. In an attempt to understand the physiological reactions of animals able to endure these extreme conditions, adaptation processes in the mussel Bathymodiolus azoricus maintained for long periods under laboratory conditions were investigated. Even in the absence of the characteristic high hydrostatic pressure found at deep-sea vent sites and without methane and/or sulphide supplementation, vent mussels seem to survive well in aquarium conditions. Therefore, the maintenance of live vent mussels in our laboratory is a key factor in gaining insights into their physiology, as well as into the study of evolutionary conserved molecules commonly found in other marine bivalves. With the aim of finding distinct genetic signatures in the expression of genes such as the metal-binding protein metallothionein (MT), the present work centred on cellular and humoral mechanisms in animals acclimatized to sea-level conditions. In addition, we also conducted experiments under hydrostatic pressure, using the hyperbaric chamber IPOCAMP to establish an in vitro experimental system in which the expression of genes that typically respond to heavy metal contaminants and oxidative stress could be studied under controlled hyperbaric pressure. We also analysed the occurrence of glycosylation in mantle and gill tissues from mussels subjected to elevated hyperbaric pressure, as well as the variation in haemocyte total counts as a result of increased pressure. Our results suggest that even after prolonged aquarium maintenance at atmospheric pressure, mussels were still able to induce the MT gene, whether or not they had been subjected to repressurization in the IPOCAMP chamber. Taken together, our results suggest that B. azoricus can be used as a model species and is particularly useful for the assessment of expression levels of critical genes, such as MT, in response to experimentally induced hydrostatic pressure.