Surfing the vegetal pole in a small population: extracellular vertical transmission of an 'intracellular' deep-sea clam symbiont.
Symbiont transmission is a key event for understanding the processes underlying symbiotic associations and their evolution. However, our understanding of the mechanisms of symbiont transmission remains still fragmentary. The deep-sea clam Calyptogena okutanii harbours obligate sulfur-oxidizing intracellular symbiotic bacteria in the gill epithelial cells. In this study, we determined the localization of their symbiont associating with the spawned eggs, and the population size of the symbiont transmitted via the eggs. We show that the symbionts are located on the outer surface of the egg plasma membrane at the vegetal pole, and that each egg carries approximately 400 symbiont cells, each of which contains close to 10 genomic copies. The very small population size of the symbiont transmitted via the eggs might narrow the bottleneck and increase genetic drift, while polyploidy and its transient extracellular lifestyle might slow the rate of genome reduction. Additionally, the extracellular localization of the symbiont on the egg surface may increase the chance of symbiont exchange. This new type of extracellular transovarial transmission provides insights into complex interactions between the host and symbiont, development of both host and symbiont, as well as the population dynamics underlying genetic drift and genome evolution in microorganisms.
Department of Marine Biodiversity Research , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Tetsuro
0000-0003-3158-2421
T
Ikuta
Department of Marine Biodiversity Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan; Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan.
Kanae
K
Igawa
Marine Works Japan, Ltd , 3-54-1 Oppamahigashi, Yokosuka, Kanagawa 237-0063 , Japan.
Akihiro
A
Tame
Department of Chemical and Biological Sciences, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo 112-8681, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
Tsuneyoshi
T
Kuroiwa
Department of Chemical and Biological Sciences, Japan Women's University, 2-8-1 Mejirodai, Bunkyo-ku, Tokyo 112-8681, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
Haruko
H
Kuroiwa
Department of Marine Biodiversity Research , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Yui
Y
Aoki
Department of Subsurface Geobiological Analysis and Research , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Yoshihiro
Y
Takaki
Department of Marine Biodiversity Research , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Yukiko
Y
Nagai
Department of Marine Biodiversity Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan; Department of Marine Biosciences, School of Marine Biosciences, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.
Genki
G
Ozawa
Department of Subsurface Geobiological Analysis and Research , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Masahiro
M
Yamamoto
Department of Biology , Miyagi University of Education , Aoba-ku, Sendai, Miyagi 980-0845 , Japan.
Ryusaku
R
Deguchi
Department of Marine Biodiversity Research , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Katsunori
K
Fujikura
Research and Development Center for Marine Biosciences , Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima, Yokosuka, Kanagawa 237-0061 , Japan.
Tadashi
T
Maruyama
Department of Marine Biodiversity Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan; Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan; Department of Marine Biosciences, School of Marine Biosciences, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.
Takao
T
Yoshida
deep-sea clam; endosymbiosis; population size; vertical transmission