Energetics of the Citric Acid Cycle in the Deep Biosphere

Peter A. Canovas, Everett L. Shock

Research output: Chapter in Book/Report/Conference proceedingChapter

3 Scopus citations


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.

Original languageEnglish (US)
Title of host publicationGeophysical Monograph Series
PublisherJohn Wiley and Sons Inc.
Number of pages25
StatePublished - 2020

Publication series

NameGeophysical Monograph Series
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

ASJC Scopus subject areas

  • Geophysics


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