12:00 PM - 12:15 PM
[BBG02-11] Deep Microbial Proliferation at Mg, Fe-Phyllosilicates in 2-Billion-Year-Old Ultramafic Rock from the Bushveld Igneous Complex, South Africa
Keywords:Origin of life, Rock-water interaction, Clay mineral, Microbe, XAFS, ESEM
The habitability of 100-million-year-old igneous rocks in the oceanic crust has been demonstrated, even though the energy supply from rock-water interactions is extremely limited (Suzuki et al., 2020). Recently, microbial colonization in a 2-billion-year-old mafic rock in the Bushveld Igneous Complex, South Africa, drilled by the International Continental Scientific Drilling Program (ICDP) has been reported (Suzuki et al., 2024). While the microbial colonization in 100-million-year-old igneous rocks is associated with Mg and Fe-phyllosilicates, the mineralogical characteristics of microbial habitats in 2-billion-year-old rocks remain poorly understood. We used previously established methods to detect indigenous and contaminant microbial cells in a rock core sample (cf. Suzuki et al., 2024), alongside conventional and advanced mineralogical characterizations. In addition, we extended the drilling depth from 15 to 800 m below ground level and the rock type from mafic to ultramafic.
Visual observation and X-ray diffraction analysis showed that the ultramafic core sample was mainly composed of pyroxene. After precision rock-thin sectioning, an epifluorescence microscope, an environmental scanning electron microscope (ESEM), and a scanning soft X-ray spectromicroscope revealed microbial colonization at pyroxene grain boundaries covered with Mg- and Fe-bearing aluminosilicate phases. Mg and Al K-edge X-ray absorption near edge structure (XANES) spectra confirmed that the aluminosilicate phases were phyllosilicates. Additionally, Fe L-edge XANES spectra indicated the presence of Fe (III), suggesting that the microbial colonization may be related to Fe (III)-based metabolism.
To evaluate this possibility, we incubated the powdered pyroxenite sample with Fe (III) solid phases (hematite and ferrihydrite) as electron acceptors, and acetate and H2 as carbon and/or energy sources. In addition, various electron acceptors such as O2, NO3-, SO42-, and CO2 were tested for the incubation experiments. After 2-week incubation, microbial growth was evident only when the Fe (III) solid phases were amended.
These lines of evidence support that Fe (III)-bearing phyllosilicate formed by low-temperature rock-water interactions could play a crucial role in microbial proliferation and survival even in two-billion-year-old pyroxenite deeply seated in the Bushveld Igneous Complex.
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
Suzuki, Y., Webb, S.J., Kouduka, M., et al. Subsurface Microbial Colonization at Mineral-Filled Veins in 2-Billion-Year-Old Mafic Rock from the Bushveld Igneous Complex, South Africa. Microb Ecol 87, 116 (2024). https://doi.org/10.1007/s00248-024-02434-8
Visual observation and X-ray diffraction analysis showed that the ultramafic core sample was mainly composed of pyroxene. After precision rock-thin sectioning, an epifluorescence microscope, an environmental scanning electron microscope (ESEM), and a scanning soft X-ray spectromicroscope revealed microbial colonization at pyroxene grain boundaries covered with Mg- and Fe-bearing aluminosilicate phases. Mg and Al K-edge X-ray absorption near edge structure (XANES) spectra confirmed that the aluminosilicate phases were phyllosilicates. Additionally, Fe L-edge XANES spectra indicated the presence of Fe (III), suggesting that the microbial colonization may be related to Fe (III)-based metabolism.
To evaluate this possibility, we incubated the powdered pyroxenite sample with Fe (III) solid phases (hematite and ferrihydrite) as electron acceptors, and acetate and H2 as carbon and/or energy sources. In addition, various electron acceptors such as O2, NO3-, SO42-, and CO2 were tested for the incubation experiments. After 2-week incubation, microbial growth was evident only when the Fe (III) solid phases were amended.
These lines of evidence support that Fe (III)-bearing phyllosilicate formed by low-temperature rock-water interactions could play a crucial role in microbial proliferation and survival even in two-billion-year-old pyroxenite deeply seated in the Bushveld Igneous Complex.
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
Suzuki, Y., Webb, S.J., Kouduka, M., et al. Subsurface Microbial Colonization at Mineral-Filled Veins in 2-Billion-Year-Old Mafic Rock from the Bushveld Igneous Complex, South Africa. Microb Ecol 87, 116 (2024). https://doi.org/10.1007/s00248-024-02434-8