Fossilized glycolipids reveal past oceanic N2 fixation by heterocystous cyanobacteria

T. Bauersachs, E.N. Speelman, E.C. Hopmans, G.-J. Reichart, S. Schouten*, J.S. Sinninghe Damsté

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


N-2-fixing cyanobacteria play an essential role in sustaining primary productivity in contemporary oceans and freshwater systems. However, the significance of N-2-fixing cyanobacteria in past nitrogen cycling is difficult to establish as their preservation potential is relatively poor and specific biological markers are presently lacking. Heterocystous N-2-fixing cyanobacteria synthesize unique long-chain glycolipids in the cell envelope covering the heterocyst cell to protect the oxygen-sensitive nitrogenase enzyme. We found that these heterocyst glycolipids are remarkably well preserved in (ancient) lacustrine and marine sediments, unambiguously indicating the (past) presence of N-2-fixing heterocystous cyanobacteria. Analysis of Pleistocene sediments of the eastern Mediterranean Sea showed that heterocystous cyanobacteria, likely as epiphytes in symbiosis with planktonic diatoms, were particularly abundant during deposition of sapropels. Eocene Arctic Ocean sediments deposited at a time of large Azolla blooms contained glycolipids typical for heterocystous cyanobacteria presently living in symbiosis with the freshwater fern Azolla, indicating that this symbiosis already existed in that time. Our study thus suggests that heterocystous cyanobacteria played a major role in adding "new" fixed nitrogen to surface waters in past stratified oceans.
Original languageEnglish
Pages (from-to)19190-19194
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number45
Publication statusPublished - 2010


  • Cyanobacterial biomarkers
  • Intact polar lipids
  • Nitrogen fixation
  • Saproprel
  • Symbiosis


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