[M-IS21] Chemosynthetic community and mud volcano: biology, geochemistry, and geophysics of fluid discharge

[MIS21-06] Dual symbiosis in the deep-sea hydrothermal vent snail Gigantopelta aegis revealed by its hologenome

*Yi Lan¹, Jin Sun^1,2, Chong Chen³, Jian-Wen Qiu⁴, Pei-Yuan Qian¹ (1.Hong Kong University of Science and Technology, 2.Ocean University of China, 3.Japan Agency for Marine-Earth Science and Technology , 4.Hong Kong Baptist University)

Keywords:chemosynthesis, sulphur-oxidising, methane-oxidising, Mollusca

Animals endemic to deep-sea hydrothermal vents often form obligatory relationships with bacterial symbionts, maintained by intricate host–symbiont interactions. Most genomic studies focusing on symbiotic systems failed to simultaneously investigate the host and symbionts to a similar depth. Here, we report novel dual symbiosis in the peltospirid snail Gigantopelta aegis with two gammaproteobacterial endosymbionts: one being a sulphur oxidiser and the other a methane oxidiser. We assembled high-quality genomes for all three parties of this holobiont, with a chromosome-level assembly for the snail host (1.15 Gb, 15 pseudo-chromosomes). In-depth analyses of these genomes revealed an intimate mutualistic relationship with complementarity in nutrition and metabolic co-dependency, resulting in a system that is highly versatile in transportation and utilisation of chemical energy. Moreover, G. aegis likely has remodelled its immune system to facilitate hosting more than one type of symbiont. Comparisons with Chrysomallon squamiferum, another chemosymbiotic snail in the same family but with only a sulphur-oxidising gammaproteobacterial endosymbiont, showed that the two snails’ sulphur-oxidising endosymbionts are phylogenetically distant. This finding was consistent with previous results that the two snails have evolved endosymbiosis independently and convergently. Notably, same capabilities in the biosynthesis of specific nutrients lacking in the host genomes are shared by the two sulphur-oxidising endosymbionts of the two snail genera, which may be a key criterion in symbiont selection by the hosts.