Hologenome analysis reveals dual symbiosis in the deep-sea hydrothermal vent snail Gigantopelta aegis

Animals endemic to deep-sea hydrothermal vents often form obligatory symbioses with bacteria, maintained by intricate host-symbiont interactions. Most genomic studies on holobionts have not investigated both sides to similar depths. Here, we report dual symbiosis in the peltospirid snail Gigantopelta aegis with two gammaproteobacterial endosymbionts: a sulfur oxidiser and a methane oxidiser. We assemble high-quality genomes for all three parties, including a chromosome-level host genome. Hologenomic analyses reveal mutualism with nutritional complementarity and metabolic co-dependency, highly versatile in transporting and using chemical energy. Gigantopelta aegis likely remodels its immune system to facilitate dual symbiosis. Comparisons with Chrysomallon squamiferum, a confamilial snail with a single sulfur-oxidising gammaproteobacterial endosymbiont, show that their sulfur-oxidising endosymbionts are phylogenetically distant. This is consistent with previous findings that they evolved endosymbiosis convergently. Notably, the two sulfur-oxidisers share the same capabilities in biosynthesising nutrients lacking in the host genomes, potentially a key criterion in symbiont selection. Symbiotic partners are rarely studied in equal depth. By assembling new genomes, Lan et al. report a novel dual symbiosis in the snail Gigantopelta aegis with two evolutionarily distant gammaproteobacterial endosymbionts: one which oxidises sulfur, the other, methane in a metabolically mutualistic relationship.

Automated summary

This study reports a novel dual symbiosis in the snail Gigantopelta aegis with two evolutionarily distant gammaproteobacterial endosymbionts: one sulfur oxidising and the other methane oxidising. The hologenomic analyses reveal a metabolically mutualistic relationship with nutritional complementarity and metabolic co-dependency. The host likely remodels its immune system to facilitate the dual symbiosis.