The endolithic environment, the pore space of rocks, is a ubiquitous habitat for microorganisms on the Earth1 and is an important target of the search for life elsewhere in the Solar System2. Photosynthetic, endolithic microbial communities commonly inhabit the outer millimetres to centimetres of all rocks exposed to the Earth's surface. In the most extreme terrestrial climates, such as hot and cold deserts, endolithic microorganisms are often the main form of life3,4,5. The endolithic microhabitat gives protection from intense solar radiation and desiccation, and it provides mineral nutrients, rock moisture and growth surfaces4,5. Here we describe the discovery and identification of the constituents of an extremely acidic (pH 1) endolithic microbial community inhabiting the pore space of rocks in the geothermal environment of Yellowstone National Park, USA. Subjected to silica mineralization, such endolithic communities constitute biomarkers that can become fossilized and potentially preserved in the geological record. Remnants of these communities could serve as biosignatures and provide important clues about ancient life associated with geothermal environments on the Earth or elsewhere in the Solar System.
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We thank K. Harris, D. Papineau, R. Ley, C. Rumbaitis-del Rio and the Pace laboratory members for discussion; H. Haesler, C. Hendrix and the staff of Yellowstone National Park for their assistance and discussion; J. Maresca and D. Bryant for high-performance liquid chromatography analysis of photosynthetic pigments; F. Luiszer and J. Drexler for chemical analysis and support for SEM; P. Boni and T. Giddings for sample preparation; H. Kleebe and G. Zito of the Colorado School of Mines for use of the BSE–SEM; and R. Castenholz and the CCMEE for cultures of Cyanidium spp. This research was supported by a grant from the NSF to N.R.P. and the University of Colorado Center for Astrobiology.
The authors declare that they have no competing financial interests.
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Walker, J., Spear, J. & Pace, N. Geobiology of a microbial endolithic community in the Yellowstone geothermal environment. Nature 434, 1011–1014 (2005). https://doi.org/10.1038/nature03447
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