14:05 〜 14:20
[BBG01-02] Microbial communities in brucite-carbonate chimneys and clam colony sediments in the Shinkai Seep Field, the deepest serpentinite-hosted vent system in the Southern Mariana Forearc
キーワード：蛇紋岩化反応、チムニー、堆積物、シロウリガイコロニー
Chemosynthetic ecosystems associated with serpentinization reactions have attracted much attention in recent years as an analog of the biosphere of the early Earth and extraterrestrial planets. The Shinkai Seep Field, discovered in 2010 at a depth of about 5700 m on the landward slope of the Southern Mariana Forearc (Ohara et al., 2012), is the world's deepest seep site associated with serpentinization reactions. A total of five chimney-dense sites and 13 clam colony sites were discovered during the past explorations, and they were characterized by a diverse faunal community of Calyptogena, snails, and polychaetes (Okumura et al., 2016), compared to other sites. In this study, we analyzed the prokaryotic SSU rRNA gene tag sequence of one sediment core sample (4 sections), four samples (11 sections) of two types of chimneys identified in previous studies, and precipitates attached on markers placed on the cuttings of the chimneys for one year (2 sections), in order to identify the chemosynthetic microorganisms that are thought to support this ecosystem.
Previous studies have described two types of chimneys: those rich in brucite and growing rapidly in relatively active seeping alkaline fluid (Type 1), and those with a higher calcium carbonate content, the dense surface cover of polychaetes and snails, and slow growth in relatively calm seeping (Type 2). In the alpha diversity analysis, Type 1 chimneys and marker sediments, which are considered to be heavily supplied with alkaline fluids, have relatively low diversity and higher fluid supply (Okumura et al., 2016). LEfSe analysis pick upped marker phylotypes sulfur-oxidizing bacteria, methane-oxidizing bacteria, methanogenic archaea were found in the Type I chimney and marker precipitates, methylotrophic bacteria in the Type II chimney, and sulfate-reducing bacteria and sulfur-oxidizing bacteria in sediments. In this seep field, it is clear that diverse geochemical conditions cause differences in microbial communities due to differences in the supply of alkaline fluid related to serpentinization. This background is thought to support a high-density faunal community not found at other sites.
References
[1] Ohara et al. (2012) Proc. Natl. Acad. Sci. U. S. A., 109, 2831–2835.
[2] Okumura et al. (2016) Geochem. Geophys. Geosys. 17, 3775–3796.
Previous studies have described two types of chimneys: those rich in brucite and growing rapidly in relatively active seeping alkaline fluid (Type 1), and those with a higher calcium carbonate content, the dense surface cover of polychaetes and snails, and slow growth in relatively calm seeping (Type 2). In the alpha diversity analysis, Type 1 chimneys and marker sediments, which are considered to be heavily supplied with alkaline fluids, have relatively low diversity and higher fluid supply (Okumura et al., 2016). LEfSe analysis pick upped marker phylotypes sulfur-oxidizing bacteria, methane-oxidizing bacteria, methanogenic archaea were found in the Type I chimney and marker precipitates, methylotrophic bacteria in the Type II chimney, and sulfate-reducing bacteria and sulfur-oxidizing bacteria in sediments. In this seep field, it is clear that diverse geochemical conditions cause differences in microbial communities due to differences in the supply of alkaline fluid related to serpentinization. This background is thought to support a high-density faunal community not found at other sites.
References
[1] Ohara et al. (2012) Proc. Natl. Acad. Sci. U. S. A., 109, 2831–2835.
[2] Okumura et al. (2016) Geochem. Geophys. Geosys. 17, 3775–3796.