Hydrogen isotope composition of Thermoanaerobacterium saccharolyticum lipids: Comparing wild type with a nfn- transhydrogenase mutant

The 2H/1H ratio in microbial fatty acids can record information about the energy metabolism of microbes and about the isotopic composition of environmental water. However, the mechanisms involved in the fractionation of hydrogen isotopes between water and lipid are not fully resolved. We provide data aimed at understanding this fractionation in the Gram-positive, obligately thermophilic anaerobe Thermoanaerobacterium saccharolyticum, by comparing a wild-type strain with a deletion mutant in which the nfnAB genes encoding electron-bifurcating transhydrogenase have been removed. The wild strain showed faster growth rate and larger overall fractionation (2εtotal −319 ± 4‰) than the mutant strain (2εtotal −298 ± 4‰). The overall trend in growth rate and fractionation, along with the isotopic ordering of individual lipids, is consistent with results reported for the Gram-negative sulfate reducer, Desulfovibrio alaskensis G20.