AbstractAnimals endemic to deep-sea hydrothermal vents often form obligatory relationships with bacterial symbionts, maintained by intricate host-symbiont interactions. Endosymbiosis with more than one symbiont is uncommon, and most genomic studies focusing on such ‘dual symbiosis’ systems have not investigated the host and the symbionts to a similar depth simultaneously. Here, we report a novel dual symbiosis among the peltospirid snail Gigantopelta aegis and its two Gammaproteobacteria 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, N50 = 82 Mb, 15 pseudo-chromosomes). In-depth analyses of these genomes reveal an intimate mutualistic relationship with complementarity in nutrition and metabolic codependency, resulting in a system highly versatile in transportation and utilisation of chemical energy. Moreover, G. aegis has an enhanced immune capability that likely facilitates the possession of more than one type of symbiont. Comparisons with Chrysomallon squamiferum, another chemosymbiotic snail in the same family but only with one sulphur-oxidising endosymbiont, show that the two snails’ sulphur-oxidising endosymbionts are phylogenetically distant, agreeing with previous results that the two snails have evolved endosymbiosis independently and convergently. Notably, the same capabilities of biosynthesis of specific nutrition lacking in the host genome are shared by the two sulphur-oxidising endosymbionts of the two snail genera, which may be a key criterion in the selection of symbionts by the hosts.
Citation
Lan, Y., Sun, J., Chen, C., Sun, Y., Zhou, Y., Yang, Y., … Qian, P.-Y. (2020). Dual symbiosis in the deep-sea hydrothermal vent snail Gigantopelta aegis revealed by its hologenome. doi:10.1101/2020.09.23.308304
Acknowledgements
We thank captain and crew of the R/V Xiangyanghong 9 and pilots of HOV Jiaolong for their great support during the research cruise DY35th-II, and captain and crew of the R/V Dayang Yihao as well as the operation team of the ROV Sea Dragon III during the third leg of the China Ocean Mineral Resources Research and Development Association DY52nd cruise. Dr. Jack C.H. Ip and Dr. Ting Xu from the Hong Kong Baptist University are gratefully acknowledged for their helpful comments. This work was supported by grants from China
Ocean Mineral Resources Research and Development Association (DY135-E2-1-03), the Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (SMSEGL20SC01), Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0409), and Major Project of Basic and Applied Basic Research of Guangdong Province (2019B030302004-04) awarded to P-YQ.
