Host-microbe interactions in deep-sea invertebrate holobionts

The rich diversity of chemosymbiotic animals are most common in deep-sea chemosynthesis-based ecosystems, and represent a pinnacle of harmonic coexistence between microbes and metazoans. However, the molecular mechanisms of such symbiosis are still largely unclear. Especially, some host animals still possess a functional gut that can be considered as a critical mixotrophic dependency in such holobionts. Uncovering the complex interactions among the symbiotic parties is key to understanding how they cooperate as a single metabolically balanced unit – holobiont. Here, simultaneous and comprehensive analyses of the hologenome, holotranscriptome, and holoproteome of deep-sea chemosymbiotic invertebrates were conducted, to unravel host-microbiota interactions. This collection contribute to understanding the evolution, ecological and health effects of microorganisms on the host and developing a suitable toolbox to better characterize deep-sea chemosymbiosis. In a typical endosymbiosis model, the interdependence between Paraescarpia echinospica and its symbionts was revealed by mutual nutrient provisions, regulation, and constraints, which is a key adaptation allowing the tubeworm to thrive in cold-seep chemosynthetic ecosystems. Genomic comparisons of vestimentiferan endosymbionts showed that the seep-living siboglinid endosymbionts are more prone than the vent-dwelling siboglinid endosymbionts to resist environmental stress and use pathogen-like mechanisms to evade host immune responses to survive intracellularly. Furthermore, the endosymbiont of Paraescarpia echinospica may be able to degrade host proteins, and the endosymbiont is believed to have evolved strategies to mediate host innate immunity. Overall, the results shed light on the host-symbiont interactions in maintaining symbiosis in deep-sea tubeworms and underline the differences between and within symbionts of vent and seep tubeworm species on the whole genome level. In a semi-endosymbiosis model, the previous