Cold-induced metabolic conversion of haptophyte di- to tri-unsaturated C37 alkenones used as palaeothermometer molecules

• Kitamura, Eri

• Kotajima, Tomonori

• Sawada, Ken

• SUZUKI, Iwane

• Shiraiwa, Yoshihiro

Abstract

The cosmopolitan marine haptophyte alga Emiliania huxleyi accumulates very long-chain (C 37 -C 40 ) alkyl ketones with two to four trans -type carbon-carbon double bonds (alkenones). These compounds are used as biomarkers of haptophytes and as palaeothermometers for estimating sea-surface temperatures in biogeochemistry. However, the biosynthetic pathway of alkenones in algal cells remains enigmatic, although it is well known that the C 37 tri-unsaturated alkenone (K 37:3 ) becomes dominant at low temperatures, either by desaturation of K 37:2 or by a separate pathway involving the elongation of tri-unsaturated alkenone precursors. Here, we present experimental evidence regarding K 37:3 synthesis. Using the well-known cosmopolitan alkenone producer E . huxleyi , we labelled K 37:2 with 13 C by incubating cells with 13 C-bicarbonate in the light at 25 °C under conditions of little if any K 37:3 production. After stabilisation of the 13 C-K 37:2 level by depleting 13 C-bicarbonate from the medium, the temperature was suddenly reduced to 15 °C. The 13 C-K 37:2 level rapidly decreased, and the 13 C-K 37:3 level increased, whereas the total 13 C-K 37 level—namely [K 37:2  + K 37:3 ]—remained constant. These 13 C-pulse-chase-like experimental results indicate that 13 C-K 37:2 is converted directly to 13 C-K 37:3 by a desaturation reaction that is promoted by a cold signal. This clear-cut experimental evidence is indicative of the existence of a cold-signal-triggered desaturation reaction in alkenone biosynthesis.

Journal

• Scientific Reports

  Scientific Reports 8 2196-, 2018-02

  Nature Publishing Group

Keywords

• Multidisciplinary

Details

• CRID: 1050282677537438336
• NII Article ID: 120007134458
• DOI: 10.1038/s41598-018-20741-2
• ISSN: 20452322
• HANDLE: 2241/00151188
• Web Site: https://tsukuba.repo.nii.ac.jp/records/45907
• Web Site: https://www.nature.com/articles/s41598-018-20741-2
• Web Site: https://www.nature.com/articles/s41598-018-20741-2.pdf
• Text Lang: en
• Article Type: journal article
• Data Source:
  • IRDB
  • Crossref
  • CiNii Articles
  • KAKEN