Long-isolated subsurface brine environments (Ma-Ga residence times) may be habitable if they sustainably provide substrates, e.g. through water-rock reaction, that support microbial catabolic energy yields exceeding maintenance costs.
![Images of cells via optical microscopy for 95-level (a), and via fluorescence microscopy combined with SYTO-9 staining for the (b) 101-level, (c) 1200-level, and (d) service water. Scale bar on the lower right of each image represents 5 μm. Magnification was 50x for (a) and 1000x for (b), (c) and (d). Cells in (a) are circular features entrapped in halite fluid inclusions and identified by red arrows. Cells in (b), (c), and (d) appear as bright green shapes. In (b), green background fluorescence highlights the high level of dissolved organic carbon debris for this sample [29]. Cell counts for the 95-, 101-, service water, and 1200-levels were 102 cells/mL ±10, 104 cells/mL ± 102, 106 cells/mL ± 104.5, 105 cells/mL ±103.3, respectively (error in standard deviation). A schematic is included to the right showing the depth and major lithology of fluid sampling sites considered in this study. -- ISME Communications](https://i0.wp.com/astrobiology.com/wp-content/uploads/2024/11/Radiolytic-Support-For-Oxidative-Metabolism-In-An.png?resize=1200%2C719&ssl=1)
Long-isolated subsurface brine environments (Ma-Ga residence times) may be habitable if they sustainably provide substrates, e.g. through water-rock reaction, that support microbial catabolic energy yields exceeding maintenance costs.