TY - JOUR
T1 - Stable Carbon Isotope Depletions in Lipid Biomarkers Suggest Subsurface Carbon Fixation in Lava Caves
AU - Selensky, Matthew J.
AU - Masterson, Andrew L.
AU - Blank, Jennifer G.
AU - Lee, Sohyun C.
AU - Osburn, Magdalena R.
N1 - Funding Information:
This work was supported by Biologic and Resource Analog Investigations in Low-Light Environments (BRAILLE; NNH16ZDA001N), a project funded by the NASA Planetary Science and Technology Analog Research (PSTAR) program. Samples were collected under permit numbers LABE-2017-SCI-028, LABE-2018-SCI-0008, and LABE-2019-SCI-0012. We sincerely thank Randy Paynor, Katrina Smith, David Hayes, and Patricia Seiser for permitting and field support and all other park staff at Lava Beds National Monument for facilitating this study. MRO is a fellow in the CIFAR Earth 4D program.
Funding Information:
This work was supported by Biologic and Resource Analog Investigations in Low‐Light Environments (BRAILLE; NNH16ZDA001N), a project funded by the NASA Planetary Science and Technology Analog Research (PSTAR) program. Samples were collected under permit numbers LABE‐2017‐SCI‐028, LABE‐2018‐SCI‐0008, and LABE‐2019‐SCI‐0012. We sincerely thank Randy Paynor, Katrina Smith, David Hayes, and Patricia Seiser for permitting and field support and all other park staff at Lava Beds National Monument for facilitating this study. MRO is a fellow in the CIFAR Earth 4D program.
Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.
PY - 2021/7
Y1 - 2021/7
N2 - Lava caves, formed through basaltic volcanism, are accessible conduits into the shallow subsurface and the microbial life residing there. While evidence for this life is widespread, the level of dependence of these microbial communities on surface inputs, especially that of organic carbon (OC), is a persistent knowledge gap, with relevance to both terrestrial biogeochemistry and the characterization of lava caves as Mars analog environments. Here, we explore carbon cycling processes within lava caves at Lava Beds National Monument, CA. We interrogate a range of cave features and surface soils, characterizing the isotopic composition (δ13C) of bulk organic and inorganic phases, followed by organic geochemical analysis of the distribution and δ13C signatures of fatty acids derived from intact polar lipids (IPLs). From these data, we estimate the carbon sources of different sample types, finding that surface soils and mineral-rich speleothems incorporate plant-derived biomass (δ13CVPDB ∼ −30‰), whereas biofilms are dominated by strongly 13C-depleted lipids (minimum δ13CVPDB −45.4‰) specific to bacteria, requiring a significant proportion of their biomass to derive from in situ fixation of inorganic carbon from previously respired OC. Based on the prevalence and abundance of these 13C-depleted lipids, we conclude that biofilms here are fueled by in situ chemolithoautotrophy, despite relatively high concentrations of dissolved OC in colocated cave waters. This unexpected metabolic potential mirrors that found in other deep subsurface biospheres and has significant positive implications for the potential microbial habitability of the Martian subsurface.
AB - Lava caves, formed through basaltic volcanism, are accessible conduits into the shallow subsurface and the microbial life residing there. While evidence for this life is widespread, the level of dependence of these microbial communities on surface inputs, especially that of organic carbon (OC), is a persistent knowledge gap, with relevance to both terrestrial biogeochemistry and the characterization of lava caves as Mars analog environments. Here, we explore carbon cycling processes within lava caves at Lava Beds National Monument, CA. We interrogate a range of cave features and surface soils, characterizing the isotopic composition (δ13C) of bulk organic and inorganic phases, followed by organic geochemical analysis of the distribution and δ13C signatures of fatty acids derived from intact polar lipids (IPLs). From these data, we estimate the carbon sources of different sample types, finding that surface soils and mineral-rich speleothems incorporate plant-derived biomass (δ13CVPDB ∼ −30‰), whereas biofilms are dominated by strongly 13C-depleted lipids (minimum δ13CVPDB −45.4‰) specific to bacteria, requiring a significant proportion of their biomass to derive from in situ fixation of inorganic carbon from previously respired OC. Based on the prevalence and abundance of these 13C-depleted lipids, we conclude that biofilms here are fueled by in situ chemolithoautotrophy, despite relatively high concentrations of dissolved OC in colocated cave waters. This unexpected metabolic potential mirrors that found in other deep subsurface biospheres and has significant positive implications for the potential microbial habitability of the Martian subsurface.
KW - biofilms
KW - carbon cycling
KW - cave biospheres
KW - compound-specific fatty acid isotopes
KW - stable carbon isotopes
KW - subsurface
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U2 - 10.1029/2021JG006430
DO - 10.1029/2021JG006430
M3 - Article
AN - SCOPUS:85111609957
VL - 126
JO - Journal of Geophysical Research: Biogeosciences
JF - Journal of Geophysical Research: Biogeosciences
SN - 2169-8953
IS - 7
M1 - e2021JG006430
ER -