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ISME J. 2014 Jan;8(1):40-51. doi: 10.1038/ismej.2013.131. Epub 2013 Aug 8.

Allying with armored snails: the complete genome of gammaproteobacterial endosymbiont.

Author information

1
1] Laboratory of Microbiology, Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan [2] Subsurface Geobiology Advanced Research (SUGAR) Project, Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
2
Subsurface Geobiology Advanced Research (SUGAR) Project, Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan.
3
Cooperative Research Project for Extremophiles, Institute of Biogeosciences, JAMSTEC, Yokosuka, Japan.
4
Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan.
5
Laboratory of Microbiology, Faculty of Fisheries Sciences, Hokkaido University, Hakodate, Japan.
6
1] Laboratory of Advanced Chemical Biology, Graduate School of Life Science, Hokkaido University, Sapporo, Japan [2] Amino Up Chemical Company, Sapporo, Japan.
7
Enoshima Aquarium, Fujisawa, Japan.
8
1] Laboratory of Advanced Chemical Biology, Graduate School of Life Science, Hokkaido University, Sapporo, Japan [2] Medicinal Chemistry Pharmaceuticals, Co. Ltd., Sapporo, Japan.
9
Marine Biodiversity Research Program, JAMSTEC, Yokosuka, Japan.

Abstract

Deep-sea vents harbor dense populations of various animals that have their specific symbiotic bacteria. Scaly-foot gastropods, which are snails with mineralized scales covering the sides of its foot, have a gammaproteobacterial endosymbiont in their enlarged esophageal glands and diverse epibionts on the surface of their scales. In this study, we report the complete genome sequencing of gammaproteobacterial endosymbiont. The endosymbiont genome displays features consistent with ongoing genome reduction such as large proportions of pseudogenes and insertion elements. The genome encodes functions commonly found in deep-sea vent chemoautotrophs such as sulfur oxidation and carbon fixation. Stable carbon isotope ((13)C)-labeling experiments confirmed the endosymbiont chemoautotrophy. The genome also includes an intact hydrogenase gene cluster that potentially has been horizontally transferred from phylogenetically distant bacteria. Notable findings include the presence and transcription of genes for flagellar assembly, through which proteins are potentially exported from bacterium to the host. Symbionts of snail individuals exhibited extreme genetic homogeneity, showing only two synonymous changes in 19 different genes (13 810 positions in total) determined for 32 individual gastropods collected from a single colony at one time. The extremely low genetic individuality in endosymbionts probably reflects that the stringent symbiont selection by host prevents the random genetic drift in the small population of horizontally transmitted symbiont. This study is the first complete genome analysis of gastropod endosymbiont and offers an opportunity to study genome evolution in a recently evolved endosymbiont.

PMID:
23924784
PMCID:
PMC3869010
DOI:
10.1038/ismej.2013.131
[Indexed for MEDLINE]
Free PMC Article
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