Molecular analyses of the gill symbiosis of the bathymodiolin mussel Gigantidas platifrons

Although the deep-sea bathymodiolin mussels have been intensively studied as a model of animal-bacteria symbiosis, it remains challenging to assess the host-symbiont interactions due to the complexity of the symbiotic tissue—the gill. Using cold-seep mussel Gigantidas platifrons as a model, we isolated the symbiont harboring bacteriocytes and profiled the transcriptomes of the three major parts of the symbiosis—the gill, the bacteriocyte, and the symbiont. This breakdown of the complex symbiotic tissue allowed us to characterize the host-symbiont interactions further. Our data showed that the gill's non-symbiotic parts play crucial roles in maintaining and protecting the symbiosis; the bacteriocytes supply the symbiont with metabolites, control symbiont population, and shelter the symbiont from phage infection; the symbiont dedicates to the methane oxidation and energy production. This study demonstrates that the bathymodiolin symbiosis interacts at the tissue, cellular, and molecular level, maintaining high efficiency and harmonic chemosynthetic micro niche. [Display omitted] •Breakdown of the symbiotic tissue to characterize the deep-sea mussel symbiosis•Bacteriocytes provide the symbiont with metabolites, shelter, and population control•Non-symbiotic parts of the gill also play crucial roles in maintaining the symbiosis•The mussel and the symbiont work together to maintain the high-efficiency symbiosis Molecular Mechanism of Gene Regulation; Microbial Genomics; Mariculture