Growth, lipid production and metabolic adjustments in the euryhaline eustigmatophyte Nannochloropsis oceanica CCALA 804 in response to osmotic downshift

Dipasmita Pal, Inna Khozin-Goldberg, Shoshana Didi-Cohen, Alexei Solovchenko, Albert Batushansky, Yuval Kaye, Noga Sikron, Talya Samani, Aaron Fait, Sammy Boussiba

Research output: Contribution to journalArticlepeer-review

56 Scopus citations

Abstract

We investigated the effects of osmotic downshift induced by the transfer of Nannochloropsis oceanica CCALA 804 from artificial seawater medium (27 g L -1 NaCl) to the same medium without NaCl or freshwater modified BG-11 medium (mBG-11) as a function of photosynthetically active radiation (170, 350, or 700 μmol photon m-2 s-1). Alterations in growth, total fatty acid (FA) content and FA composition of individual lipid classes, and in relative contents of metabolites relevant to osmotic adjustments were studied. Cells displayed remarkable tolerance to the osmotic downshift apart from some swelling, with no substantial lag or decline in cell division rate. Biomass accumulation and chlorophyll a content were enhanced upon downshifting, especially under the highest irradiance. The highest chlorophyll a and eicosapentaenoic acid (EPA) biomass and culture contents were determined in the cultures grown in mBG-11. Two days after transfer to 0 g L-1 NaCl, the proportion in total acyl lipids of the major chloroplast galactolipid monogalactosyldiacylglycerol, a major depot of EPA, increased twofold, along with a modest change in the proportion of digalactosyldiacylglycerol (DGDG). EPA percentage decreased in DGDG and increased in the extraplastidial lipid phosphatidylethanolamine. Metabolite profiling by GC-MS analysis revealed a sharp decrease in metabolites potentially involved in osmoregulation, such as mannitol and proline, while proline-cycle intermediates and some free sugars increased. The stress-induced polyamine spermidine decreased ca. one order of magnitude, while its catabolic product - the non-protein amino acid γ-amino butyric acid - increased twofold, as did the stress-related sugars trehalose and talose. Biochemical mechanisms governing osmotic plasticity and implications for optimization of EPA production by N. oceanica CCALA 804 under variable cultivation conditions are discussed.

Original languageEnglish
Pages (from-to)8291-8306
Number of pages16
JournalApplied Microbiology and Biotechnology
Volume97
Issue number18
DOIs
StatePublished - 1 Sep 2013

Keywords

  • EPA
  • Euryhaline microalga
  • MGDG
  • Nannochloropsis
  • Osmolyte
  • Salinity
  • TFA

ASJC Scopus subject areas

  • Biotechnology
  • Applied Microbiology and Biotechnology

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