10:45 AM - 12:15 PM
[BCG06-P01] Microbe-water-rock interactions in basaltic lava with olivine xenocrysts from a petit-spot volcano
Keywords:life in rock, olivine, smectite, 16S rRNA gene amplicon analysis,, Nitrosopumilus
The upper oceanic crust is composed of basaltic lava formed at the mid-oceanic ridge. Microbiological studies have revealed that microbial communities are sustained in fractures/veins up to ~100 Ma basaltic basements of mid-ocean ridge origin (Suzuki et al., 2020). The oceanic crust moves to an abyssal plain at the ages >100 Myr, where characteristic water depths range down to 6,000 m. The abyssal plain is isolated from nutrient supply from the continents, resulting in limited photosynthesis at its ocean surface and a slow sedimentation rate of plektonic debris. They all result in extreme oligotrophic conditions on the seafloor in the abyssal plain. Although the abyssal plain is static, exceptional portions are observable where the oceanic plate swells in response to bending force before the plate subducts into the mantle. This swell zone is called outer rise. In the northwestern Pacific region where the oceanic crust is older than 100 Myr, alkaline basaltic magmas periodically and locally erupted, and form submarine volcanoes, called “petit-spots”. The petit-spot magmas contain significant amounts of carbon dioxide and water. These volatiles contributed to forming bubbles in the petit-spot magmas during their ascent to the surface. In places, peridotite xenoliths and olivine xenocrysts, i.e., fragmented mantle materials, are included in the petit-spot basalts. High vesicularity of the petit-spot basalts contributes to promoting low-temperature reactions between the inclusions of mantle materials and seawater, which in turn supply energy to unique deep-sea microbial communities. In this study, we applied a method developed by Suzuki et al. (2020) to olivine xenocryst-bearing petit-spot basalt to elucidate the microbe-water-rock interactions.
Petit-spot basalt samples were collected from a petit-spot knoll at Site B (37'37.5'N, 149'30.4 'E, ~5900 m below sea level), using the deep-submergence vehicle, Shinkai 6500 during YK21-07S cruise. The basalt samples contained olivine xenocrysts up to 3 mm in diameter and numerous bubbles up to 5 mm in diameter. Some of the bubbles were filled with ochre-colored particles of seafloor sediment origin. Orange-colored olivine-xenocrysts dominated in the outer rim of the basalt samples, while green-colored olivine-xenocrysts dominated in the inner core. Microbiome data showed that total cell numbers in the outer rim and the inner core were respectively 1.9 × 106 cells/cm3 and 3.9 × 105 cells/cm3. Since these values are higher than those in the deep seawaters (103–104 cells/ml), it is evident that microbes are incubated in the petit-spot basalts. DNA extracted from the basalt sample was subjected to 16S rRNA gene amplicon analysis. Archaea of the family Nitrosopumilaceae accounted for 14.3% of the total prokaryotic populations. The most abundant sequence of Nitrosopumilaceae had a sequence identity of 93% to the aerobic autotroph Nitrosopumilus piranensis. The second abundant family was Woeseiaceae, accounting for 6.4% of the total prokaryotic populations. The most abundant sequence of Woeseiaceae was closely related to the facultatively anaerobic heterotroph Woeseia oceani with 95% similarity. 3.1 % of sequences were classified as the family Magnetospiraceae. These results suggest the presence of phylogenetically and physiologically diverse microbial populations in the basalt sample. Thin sections stained with SYBR Green I were observed with an epifluorescence microscope to reconstruct microbial cell distribution in the same basalt sample. Microbial cells were distributed at cracks in the olivine-xenocrysts and in the altered minerals in the vacancies. We will present additional analytical results from minerals coexisting with the microbial cells.
Suzuki, Y., Yamashita, S., Kouduka, M,. et al. Deep microbial proliferation at the basalt interface in 33.5–104 million-year-old oceanic crust. Commun Biol 3, 136 (2020). https://doi.org/10.1038/s42003-020-0860-1
Petit-spot basalt samples were collected from a petit-spot knoll at Site B (37'37.5'N, 149'30.4 'E, ~5900 m below sea level), using the deep-submergence vehicle, Shinkai 6500 during YK21-07S cruise. The basalt samples contained olivine xenocrysts up to 3 mm in diameter and numerous bubbles up to 5 mm in diameter. Some of the bubbles were filled with ochre-colored particles of seafloor sediment origin. Orange-colored olivine-xenocrysts dominated in the outer rim of the basalt samples, while green-colored olivine-xenocrysts dominated in the inner core. Microbiome data showed that total cell numbers in the outer rim and the inner core were respectively 1.9 × 106 cells/cm3 and 3.9 × 105 cells/cm3. Since these values are higher than those in the deep seawaters (103–104 cells/ml), it is evident that microbes are incubated in the petit-spot basalts. DNA extracted from the basalt sample was subjected to 16S rRNA gene amplicon analysis. Archaea of the family Nitrosopumilaceae accounted for 14.3% of the total prokaryotic populations. The most abundant sequence of Nitrosopumilaceae had a sequence identity of 93% to the aerobic autotroph Nitrosopumilus piranensis. The second abundant family was Woeseiaceae, accounting for 6.4% of the total prokaryotic populations. The most abundant sequence of Woeseiaceae was closely related to the facultatively anaerobic heterotroph Woeseia oceani with 95% similarity. 3.1 % of sequences were classified as the family Magnetospiraceae. These results suggest the presence of phylogenetically and physiologically diverse microbial populations in the basalt sample. Thin sections stained with SYBR Green I were observed with an epifluorescence microscope to reconstruct microbial cell distribution in the same basalt sample. Microbial cells were distributed at cracks in the olivine-xenocrysts and in the altered minerals in the vacancies. We will present additional analytical results from minerals coexisting with the microbial cells.
Suzuki, Y., Yamashita, S., Kouduka, M,. et al. Deep microbial proliferation at the basalt interface in 33.5–104 million-year-old oceanic crust. Commun Biol 3, 136 (2020). https://doi.org/10.1038/s42003-020-0860-1