4.4 Article

Inverse hydrogen isotope fractionation indicates heterotrophic microbial production of long-chain n-alkyl lipids in desolate Antarctic ponds

Journal

GEOBIOLOGY
Volume 19, Issue 4, Pages 394-404

Publisher

WILEY
DOI: 10.1111/gbi.12441

Keywords

East Antarctic ponds; heterotrophic microbes; inverse hydrogen isotopic fractionation; n‐ alkanes; n‐ alkanoic acids

Funding

  1. National Natural Science Foundation of China [41776188, 41976191, 41576183]
  2. Chinese Academy of Sciences [XDB40000000]
  3. Fundamental Research Funds for the Central Universities
  4. National Science Foundation of United States [EAR-1762431]

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Recent studies have found long-chain n-alkanes and n-alkanoic acids in sediments of desolate Antarctic ponds without vascular plants, displaying hydrogen isotopic values up to 300 per mil higher than lake water. This strongly inverse isotopic fractionation is believed to be predominantly produced by heterotrophic micro-organisms, based on experimental data. This represents the first clear example of heterotrophic microbial production of long-chain n-alkyl waxes in a natural environment.
Long-chain (>C-25) n-alkyl lipids have long been considered biomarkers for higher plant leaf waxes and widely applied for paleoclimate and paleoenvironmental reconstructions. However, recent experimental and lacustrine sediment studies suggest long-chain n-alkanes and n-alkanoic acids can also be produced by aerobic microbes, probably heterotrophic microbes based on carbon isotope data. Here we show that sedimentary long-chain n-alkanes and n-alkanoic acids in two desolate Antarctic ponds where vascular plants are absent in the surroundings display hydrogen isotopic values up to 300 per mil higher than those of lake water. It is the first time that such strongly inverse or reduced hydrogen isotopic fractionation of lipid biomarkers is observed in natural sediment samples. Based on recent extensive experimental data on microbial hydrogen isotopic fractionation, our data can only be explained by the predominant production of long-chain n-alkanes and n-alkanoic acids from heterotrophic micro-organisms. Together with preliminary 16S rRNA gene sequencing data, our results represent the first unambiguous example of predominant heterotrophic microbial production of long-chain n-alkyl waxes in a natural environment.

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