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Keywords:

  • acetogenesis;
  • isotope analysis;
  • fhs;
  • peat;
  • methanogenesis

Abstract

Acetate is a central intermediate in the anaerobic degradation of organic matter, and the resolution of its metabolism necessitates integrated strategies. This study aims to (1) estimate the contribution of acetogenesis to acetate formation in an acidic fen (pH ~ 4.9), (2) assess the genetic potential for acetogenesis targeting the fhs gene encoding formyltetrahydrofolate synthetase (FTHFS) and (3) unravel the in situ turnover of acetate using stable carbon isotope pore-water analysis. H2/CO2-supplemented peat microcosms yielded 13C-depleted acetate (−37.2‰ vs. VPDB (Vienna Peedee belemnite standard) compared with −14.2‰ vs. VPDB in an unamended control), indicating the potential for H2-dependent acetogenesis. Molecular analysis revealed a high diversity and depth-dependent distribution of fhs phylotypes with the highest number of operational taxonomic units in 0–20 cm depth, but only few and distant relationships to known acetogens. In pore waters, acetate concentrations (0–170 μM) and δ13C-values varied widely (−17.4‰ to −3.4‰ vs. VPDB) and did not indicate acetogenesis, but pointed to a predominance of sinks, which preferentially consumed 12C-acetate, like acetoclastic methanogenesis. However, depth profiles of methane and δ13CCH4 revealed a temporarily and spatially restricted role of this acetate sink and suggest other processes like sulfate and iron reduction played an important role in acetate turnover.