Geographical structure of endosymbiotic bacteria hosted by Bathymodiolus mussels at eastern Pacific hydrothermal vents

• Published in: BMC Evolutionary Biology
• Main Authors: Phuong-Thao Ho, Eunji Park, Soon Gyu Hong, Eun-Hye Kim, Kangchon Kim, Sook-Jin Jang, Robert C. Vrijenhoek, Yong-Jin Won
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2017
• Subjects: Chemosynthetic symbiosis; Deep-sea hydrothermal vent; Bathymodiolus mussels; Sulfur-oxidizing endosymbiont; Gammaproteobacteria; Geographical population structure; Evolution; QH359-425; Antarctic; Pacific; Antarc*; antarcticus
• Online Access: https://doi.org/10.1186/s12862-017-0966-3; https://doaj.org/article/7670d181cedc45c4b3f88fefd35a86a2

Abstract Background Chemolithoautotrophic primary production sustains dense invertebrate communities at deep-sea hydrothermal vents and hydrocarbon seeps. Symbiotic bacteria that oxidize dissolved sulfur, methane, and hydrogen gases nourish bathymodiolin mussels that thrive in these environments worldwide. The mussel symbionts are newly acquired in each generation via infection by free-living forms. This study examined geographical subdivision of the thiotrophic endosymbionts hosted by Bathymodiolus mussels living along the eastern Pacific hydrothermal vents. High-throughput sequencing data of 16S ribosomal RNA encoding gene and fragments of six protein-coding genes of symbionts were examined in the samples collected from nine vent localities at the East Pacific Rise, Galápagos Rift, and Pacific-Antarctic Ridge. Results Both of the parapatric sister-species, B. thermophilus and B. antarcticus, hosted the same numerically dominant phylotype of thiotrophic Gammaproteobacteria. However, sequences from six protein-coding genes revealed highly divergent symbiont lineages living north and south of the Easter Microplate and hosted by these two Bathymodiolus mussel species. High heterogeneity of symbiont haplotypes among host individuals sampled from the same location suggested that stochasticity associated with initial infections was amplified as symbionts proliferated within the host individuals. The mussel species presently contact one another and hybridize along the Easter Microplate, but the northern and southern symbionts appear to be completely isolated. Vicariance associated with orogeny of the Easter Microplate region, 2.5–5.3 million years ago, may have initiated isolation of the symbiont and host populations. Estimates of synonymous substitution rates for the protein-coding bacterial genes examined in this study were 0.77–1.62%/nucleotide/million years. Conclusions Our present study reports the most comprehensive population genetic analyses of the chemosynthetic endosymbiotic bacteria based on high-throughput ...