Premium
Hydrogen isotope fractionation during H 2 /CO 2 acetogenesis: hydrogen utilization efficiency and the origin of lipid‐bound hydrogen
Author(s) -
VALENTINE D. L.,
SESSIONS A. L.,
TYLER S. C.,
CHIDTHAISONG A.
Publication year - 2004
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1111/j.1472-4677.2004.00030.x
Subject(s) - hydrogen , fractionation , chemistry , isotope ratio mass spectrometry , stable isotope ratio , deuterium , hydrogen production , chromatography , organic chemistry , mass spectrometry , physics , quantum mechanics
Hydrogen metabolism was studied in the anaerobic bacterium, Sporomusa sp. strain DMG 58, by measuring natural abundance levels of deuterium in H 2 , H 2 O, and individual fatty acids during acetogenic growth on H 2 /CO 2 . Four cultures were grown, each in medium with a distinct hydrogen‐isotopic composition (δD‐H 2 O). The δD value of H 2 was quantified in the residual gas exiting the growth chambers and found to decrease concurrently with net H 2 consumption, indicating rapid isotope exchange between H 2 and H 2 O. An isotopic mass balance was used to constrain the efficiency with which H 2 was activated by the cell and the reducing equivalents catabolized, which we term the H 2 utilization efficiency. Results indicate that H 2 utilization efficiency in these cultures is less than 20% during the growth phase, and less than 2% after the growth phase. The gross rate of cellular H 2 activation was similar in the growth phase and afterward. Biomass harvested at the end of each experiment was used to analyse the D/H of individual membrane lipids. Values of δD were highly correlated between lipids and water (δD‐lipids = 0.59 × δD‐water – 381‰; R 2 = 0.995), indicating the source of lipid hydrogen is in isotopic equilibrium with water. Results are consistent with two possibilities: ( i ) water is the sole source of hydrogen to lipids, and the fractionation during biosynthesis is significantly larger than previously observed (α = 0.59), or ( ii ) hydrogen from H 2 is incorporated into lipids, but only after reaching isotopic equilibrium with H 2 O. Fatty acids were strongly depleted in deuterium relative to all other organisms studied thus far, and such large depletions may prove useful as biomarkers for studying H 2 cycling in anoxic environments as well as in the geological record.