@inbook{e349303b6d9c44f1991495dd5a0d730e,
title = "Energetics of the Citric Acid Cycle in the Deep Biosphere",
abstract = "Constraints on the internal composition of microbial cells are used together with standard state thermodynamic data to evaluate energy demands associated with the citric acid cycle and its individual steps to explore geobiochemical processes in the deep subsurface biosphere. Two pressure-temperature ranges are considered: up to 200 °C and to ~2 kb with the revised Helgeson-Kirkham-Flowers equations of state, and up to 200 °C from 10 to 60 kilobars with the Deep Earth Water model. The former pressure-temperature ranges encompass conditions for known life in natural systems, and the latter push the upper pressures for life into those of subduction zones using guidance from laboratory experiments. The neutral solutes H2 (aq) and CO2 (aq) can diffuse freely across cell membranes and impose external conditions into the composition of microbial cells, and as a result there is a range of chemical affinities for citric acid cycle reactions that prevail throughout the deep subsurface biosphere. These ranges raise the possibility that the citric acid cycle releases energy when run in either the forward or reverse directions depending on the affinities involved. The results of this theoretical study support the notion that life may extend far deeper into subduction zones than is generally appreciated.",
author = "Canovas, {Peter A.} and Shock, {Everett L.}",
note = "Funding Information: We thank Tucker Ely, Grayson Boyer, Alta Howells, Kirt Robinson, Kris Fecteau, Chris Glein, Kristin Johnson, Meghan Guild, Dimitri Sverjensky, and Eric Boyd for helpful conversations during the course of this research. This work was supported by grants from the Sloan Foundation to the Extreme Chemistry and Physics community of the Deep Carbon Observatory. Particular thanks are owed to Craig Manning and Wendy Mao for their patience while we prepared the results of this study for publication. Publisher Copyright: {\textcopyright} 2020 The Authors. Co-published 2020 by the American Geophysical Union and John Wiley and Sons, Inc.",
year = "2020",
doi = "10.1002/9781119508229.ch25",
language = "English (US)",
series = "Geophysical Monograph Series",
publisher = "John Wiley and Sons Inc.",
pages = "303--327",
booktitle = "Geophysical Monograph Series",
}