Thermodynamic Ecology of Hydrogen-Based Syntrophy

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens 1 1Associate editor: N. E. Ostrom

“…2) is approximately Ϫ131 kJ mol Ϫ1 under standard conditions, including 10 5 Pa H 2 . Such conditions are unusual in nature, and methanogenesis generally occurs close to the theoretical minimum free energy yield ( Lovley, 1985;Cordruwisch et al, 1988;Hoehler et al, 2001;Chong et al, 2002;Valentine, 2001) of Ϫ10 to Ϫ20 kJ mol Ϫ1 . Furthermore, catabolism is coupled to energy conservation, by way of a chemiosmotic potential (equivalent to 1 ⁄4 -1 ⁄3 of an ATP; Eqn.…”

Hydrogen isotope fractionation during H2/CO2 acetogenesis: hydrogen utilization efficiency and the origin of lipid‐bound hydrogen

“…As part of our continuing work to understand the cycling of H 2 in anoxic environments (Bilek et al ., 1999; Valentine et al ., 2000a; Valentine et al ., 2000b; Valentine, 2001; Chidthaisong et al ., 2002; Chong et al ., 2002; Valentine et al ., 2004) and the D/H composition of lipid biomarkers (Sessions et al ., 1999; Sessions et al ., 2002), we performed a series of studies designed to assess the efficiency of hydrogen utilization in active cultures of the homoacetogen, Sporomusa strain DMG 58. These studies were further designed to determine if hydrogen atoms from H 2 are incorporated into cellular lipids – potential biomarkers of H metabolism in nature.…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…This limit agrees at least roughly with in situ observations. The low energy yields of fermentation, methanogenesis, and most other forms of anaerobic metabolism suggest that anaerobic organisms function at a level of nearstarvation (Valentine, 2001).…”

“…Under anaerobic conditions, the mineralization of organic carbon to C0 2 is a multistep process that involves a consortium of organisms, each of which conserves a fraction of the potential-free energy that was available in the original organic carbon substrate. As a result, anaerobic organisms are adapted to conserve quantities of energy that often approach the theoretical minimum (20kJmol _1 ) required for metabolism (Valentine, 2001).…”