Since 1997, NASA has successfully landed five rovers on Mars. The rovers returned data indicating that life cannot survive on the Martian surface; however, we do not know if life persists underground. For underground life to continue on Mars or elsewhere, microbes would have to convert – or fix – elements from their inorganic form into a usable organic form. This skill, known as lithoautotrophy, is also useful for bacteria bound to Earth, especially microbes living in caves. These cave environments often lack nutrients due to the lack of sunlight and organic matter valued by surface life.
In a new article, Selensky et al. try to bring us closer to understanding the existence of underground alien life by exploring the carbon cycle in the lava caves at Lava Beds National Monument in California. As lava flows from a volcanic eruption, a rigid outer shell eventually solidifies as magma continues to flow inside, creating hollow tubes. Because lava tubes form through volcanism, they are presumed to exist elsewhere in the solar system, making them valuable models for planetary caving.
In California, the authors examined the carbon sources used by cave bacteria living in biofilms (stained microbial communities on cave walls), speleothems, and soil. They compared the isotopic signatures of carbon in bacterial fatty acids to carbon sources outside the cave.
Researchers have found that fatty acids produced by actinobacteria in biofilms carry isotopic signatures that cannot come from outside sources. In other words, bacteria fix carbon in situ. In contrast, bacteria from other characteristics of caves, such as speleothems, assimilate organic carbon derived from the surface.
The results suggest that some bacteria in basalt cave ecosystems fix their carbon, indicating that the microbes survive independent of the surface environment. The results challenge the paradigm according to which all the cave microbiota subsists thanks to surface inputs. Additionally, the authors claim that the findings have significant and positive implications for the search for extraterrestrial life.
Matthew J. Selensky et al, Stable carbon isotope depletions in lipid biomarkers suggest subsurface carbon uptake in lava caves, Journal of Geophysical Research: Biogeosciences (2021). DOI: 10.1029 / 2021JG006430
Provided by American Geophysical Union
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