Adaptation to deep-sea chemosynthetic environments as revealed by mussel genomes

Hydrothermal vents and methane seeps are extreme deep-sea ecosystems that support dense populations of specialised macrobenthos such as mussels. But lack of genome information hinders understanding of the adaptation of these animals to such inhospitable environment. Here we report the genomes of a deep-sea vent/seep mussel Bathymodiolus platifrons and a shallow-water mussel Modiolus philippinarum. Phylogenetic analysis shows that these mussel species diverged approximately 110.4 million years ago. Many gene families, especially those for stabilising protein structures and removing toxic substances from the cells, are greatly expanded in B. platifrons, indicating adaptation to extreme environmental conditions. The B. platifrons innate immune system is considerably more complex than that of other lophotrochozoan species including M. philippinarum, with significant expansion and high expression of gene families related to immune recognition, endocytosis and caspase-mediated apoptosis in th...