Deep Microbial Colonization in Saponite-Bearing Fractures in Aged Basaltic Crust: Implications for Subsurface Life on Mars

Abstract

One of the most promising planetary bodies that might harbor extraterrestrial life is Mars, given the presence of liquid water in the deep subsurface. The upper crust of Mars is mainly composed of >3.7-billion-year-old basaltic lava where heat-driven fluid circulation is negligible. The analogous crustal environment to the Martian subsurface is found in the Earth's oceanic crust composed of basaltic lava. The basaltic crust tends to cool down for 10–20-million-years after formation. However, microbial life in old cold basaltic lava is largely unknown even in the Earth's oceanic crust, because the lack of vigorous circulation prevents sampling of pristine crustal fluid from boreholes. Alternatively, it is important to investigate deep microbial life using pristine drill cores obtained from basaltic lava. We investigated a basaltic rock core sample with mineral-filled fractures drilled during Integral Ocean Drilling Project Expedition 329 that targeted 104-million-year-old oceanic crust. Mineralogical characterizations of fracture-infilling minerals revealed that fractures/veins were filled with Mg-rich smectite called saponite and calcium carbonate. The organic carbon content from the saponite-rich clay fraction in the core sample was 23 times higher than that from the bulk counterpart, which appears to be sufficient to supply energy and carbon sources to saponite-hosted life. Furthermore, a newly developed method to detect microbial cells in a thin-section of the saponite-bearing fracture revealed the dense colonization of SYBR-Green-I stained microbial cells spatially associated with saponite. These results suggest that the presence of saponite in old cold basaltic crust is favorable for microbial life. In addition to carbonaceous chondrite, saponite is a common product of low-temperature reactions between water and mafic minerals on Earth and Mars. It is therefore expected that deep saponite-bearing fractures could host extant life and/or the past life on Mars.

Ultra-small cells and DPANN genome unveiled inside an extinct vent chimney

“…Analytical procedures have been developed to visualize and quantify microbial cells hosted in crack-infilling minerals in the oceanic crust by preparing thin sections of rocks embedded in hydrophilic resin called LR White 8,9 . Microbial cells embedded in the resin are stainable with a DNA dye called SYBR-Green I.…”

Urea-Assisted Synthesis and Characterization of Saponite with Different Octahedral (Mg, Zn, Ni, Co) and Tetrahedral Metals (Al, Ga, B), a Review

“…The choice of saponite is based on studies that show Fe-rich saponite were able to promote and preserve precursors of biopolymers and this may have contributed to prebiotic chemistry on Earth and the deep biosphere [17]. Sueoka et al studied the mineral-filled fractures of a basaltic rock core sample obtained during the Integral Ocean Drilling Project Expedition 329 and found that these minerals were rich in Mg-rich saponite and calcium carbonate [23]. The saponite-rich clay fraction in the core contains a much higher organic carbon than the bulk counterpart suggesting enough supply of energy and carbon sources for a saponite-hosted life [23].…”

“…Sueoka et al studied the mineral-filled fractures of a basaltic rock core sample obtained during the Integral Ocean Drilling Project Expedition 329 and found that these minerals were rich in Mg-rich saponite and calcium carbonate [23]. The saponite-rich clay fraction in the core contains a much higher organic carbon than the bulk counterpart suggesting enough supply of energy and carbon sources for a saponite-hosted life [23]. Apart from the possible contributions of saponites to early life, another reason for the interest in the system is the observation that saponites are easy to synthesize and their structures can be functionalized and modulated to obtain a wide variety of interesting novel advanced layered materials for use in heterogeneous catalysis [17] or for protection of organic compounds from photolysis [24].…”

Urea-Assisted Synthesis and Characterization of Saponite with Different Octahedral (Mg, Zn, Ni, Co) and Tetrahedral Metals (Al, Ga, B), A Review

“…The choice of saponite is based on studies that show Fe-rich saponite were able to promote and preserve precursors of biopolymers and this may have contributed to prebiotic chemistry on Earth and the deep biosphere [17]. Sueoka et al studied the mineral-filled fractures of a basaltic rock core sample obtained during Integral Ocean Drilling Project Expedition 329 and found that these minerals were rich in Mg-rich saponite and calcium carbonate [23]. The saponite-rich clay fraction in the core contains a much higher organic carbon than the bulk counterpart suggesting enough supply of energy and carbon sources for a saponite-hosted life [23].…”

“…Sueoka et al studied the mineral-filled fractures of a basaltic rock core sample obtained during Integral Ocean Drilling Project Expedition 329 and found that these minerals were rich in Mg-rich saponite and calcium carbonate [23]. The saponite-rich clay fraction in the core contains a much higher organic carbon than the bulk counterpart suggesting enough supply of energy and carbon sources for a saponite-hosted life [23]. Apart from the possible contributions of saponites to early life, another reason for the interest in the system is the observation that saponites are easy to synthesize and their structures can be functionalized and modulated to obtain a wide variety of interesting novel advanced layered materials for use in heterogeneous catalysis [17] or for protection of organic compounds from photolysis [24].…”