Evidence for isotopic exchange during metabolism of stable-isotope- labeled formate in a methanogenic sediment

Abstract

The disappearance of stable-isotope-labeled formate in freshwater sediment from Lake Vechten was studied by gas chromatography-mass spectrometry. Both deuterium- and 13C-labeled formate were removed from pore water at a high rate (400 ± 35 [standard deviation] and 1,700 ± 600 μM h-1, respectively), with concomitant formation of nonlabeled formate. The removal rate of labeled and nonlabeled formate amounted to 240 ± 15 and 400 ± 40 μM h-1, respectively. The formation of nonlabeled formate is explained by isotopic exchange due to the activity of formate dehydrogenase rather than by the turnover of formate.