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 C-13- labeled formate mere removed from pore water at a high rate (400 +/- 35 [standard deviation] and 1,700 +/- 600 mu M h(-1), respectively), with concomitant formation of nonlabeled formate. The removal rate of labeled and nonlabeled formate amounted to 240 +/- 15 and 400 +/- 40 mu M 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. [KEYWORDS: Sulfate-reducing bacteria; marine sediment; acetate; turnover; hydrogen; lake]