Remodeling of intermediate metabolism in the diatom Phaeodactylum tricornutum under nitrogen stress

Orly Levitan, Jorge Dinamarca, Ehud Zelzion, Desmond S. Lun, L. Tiago Guerra, Min Kyung Kim, Joomi Kim, Benjamin A.S. Vam Mooy, Debashish Bhattacharya, Paul G. Falkowski

Research output: Contribution to journalArticlepeer-review

160 Scopus citations


Diatoms are unicellular algae that accumulate significant amounts of triacylglycerols as storage lipids when their growth is limited by nutrients. Using biochemical, physiological, bioinformatics, and reverse genetic approaches, we analyzed how the flux of carbon into lipids is influenced by nitrogen stress in a model diatom, Phaeodactylum tricornutum. Our results reveal that the accumulation of lipids is a consequence of remodeling of intermediate metabolism, especially reactions in the tricarboxylic acid and the urea cycles. Specifically, approximately one-half of the cellular proteins are cannibalized; whereas the nitrogen is scavenged by the urea and glutamine synthetase/glutamine 2-oxoglutarate aminotransferase pathways and redirected to the de novo synthesis of nitrogen assimilation machinery, simultaneously, the photobiological flux of carbon and reductants is used to synthesize lipids. To further examine how nitrogen stress triggers the remodeling process, we knocked down the gene encoding for nitrate reductase, a key enzyme required for the assimilation of nitrate. The strain exhibits 40-50% of the mRNA copy numbers, protein content, and enzymatic activity of the wild type, concomitant with a 43% increase in cellular lipid content. We suggest a negative feedback sensor that couples photosynthetic carbon fixation to lipid biosynthesis and is regulated by the nitrogen assimilation pathway. This metabolic feedback enables diatoms to rapidly respond to fluctuations in environmental nitrogen availability.

Original languageEnglish (US)
Pages (from-to)412-417
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number2
StatePublished - 2015

All Science Journal Classification (ASJC) codes

  • General


  • Lipid
  • Metabolism
  • NR
  • RNAi
  • Stress


Dive into the research topics of 'Remodeling of intermediate metabolism in the diatom Phaeodactylum tricornutum under nitrogen stress'. Together they form a unique fingerprint.

Cite this