Metabolic engineering of lipid catabolism increases microalgal lipid accumulation without compromising growth

Edited by James L. Van Etten, University of Nebraska, Lincoln, NE, and approved October 29, 2013 (received for review May 16, 2013)
November 18, 2013
110 (49) 19748-19753

Significance

As global CO2 levels rise and fossil fuel abundance decreases, the development of alternative fuels becomes increasingly imperative. Biologically derived fuels, and specifically those from microalgae, are promising sources, but improvements throughout the production process are required to reduce cost. Increasing lipid yields in microalgae without compromising growth has great potential to improve economic feasibility. We report that disrupting lipid catabolism is a practical approach to increase lipid yields in microalgae without affecting growth or biomass. We developed transgenic strains through targeted metabolic engineering that show increased lipid accumulation, biomass, and lipid yields. The target enzyme’s ubiquity suggests that this approach can be applied broadly to improve the economic feasibility of algal biofuels in other groups of microalgae.

Abstract

Biologically derived fuels are viable alternatives to traditional fossil fuels, and microalgae are a particularly promising source, but improvements are required throughout the production process to increase productivity and reduce cost. Metabolic engineering to increase yields of biofuel-relevant lipids in these organisms without compromising growth is an important aspect of advancing economic feasibility. We report that the targeted knockdown of a multifunctional lipase/phospholipase/acyltransferase increased lipid yields without affecting growth in the diatom Thalassiosira pseudonana. Antisense-expressing knockdown strains 1A6 and 1B1 exhibited wild-type–like growth and increased lipid content under both continuous light and alternating light/dark conditions. Strains 1A6 and 1B1, respectively, contained 2.4- and 3.3-fold higher lipid content than wild-type during exponential growth, and 4.1- and 3.2-fold higher lipid content than wild-type after 40 h of silicon starvation. Analyses of fatty acids, lipid classes, and membrane stability in the transgenic strains suggest a role for this enzyme in membrane lipid turnover and lipid homeostasis. These results demonstrate that targeted metabolic manipulations can be used to increase lipid accumulation in eukaryotic microalgae without compromising growth.

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Acknowledgments

We thank L. Gerwick and N. Engene (University of California, San Diego) for technical advice and M. Ohman for the Iatroscan. E.M.T. is supported by National Institutes of Health Marine Biotechnology Training Grant Fellowship 5T32GM067550. We acknowledge support by the California Energy Commission's “California Initiative for Large Molecule Sustainable Fuels,” Agreement No. 500-10-039 and additional support (to M.H.) from the Air Force Office of Scientific Research Grants FA9550-08-1-0178 and FA9550-08-1-0178, Department of Energy Grants DE-EE0001222 and DE-EE0003373, and National Science Foundation Grant CBET-0903712.

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Information & Authors

Information

Published in

Go to Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
Vol. 110 | No. 49
December 3, 2013
PubMed: 24248374

Classifications

Submission history

Published online: November 18, 2013
Published in issue: December 3, 2013

Keywords

  1. metabolism
  2. RNAi
  3. algal biofuel
  4. targeted manipulation
  5. triacylglycerol

Acknowledgments

We thank L. Gerwick and N. Engene (University of California, San Diego) for technical advice and M. Ohman for the Iatroscan. E.M.T. is supported by National Institutes of Health Marine Biotechnology Training Grant Fellowship 5T32GM067550. We acknowledge support by the California Energy Commission's “California Initiative for Large Molecule Sustainable Fuels,” Agreement No. 500-10-039 and additional support (to M.H.) from the Air Force Office of Scientific Research Grants FA9550-08-1-0178 and FA9550-08-1-0178, Department of Energy Grants DE-EE0001222 and DE-EE0003373, and National Science Foundation Grant CBET-0903712.

Notes

This article is a PNAS Direct Submission.

Authors

Affiliations

Emily M. Trentacoste
Scripps Institution of Oceanography, and
Roshan P. Shrestha
Scripps Institution of Oceanography, and
Sarah R. Smith
Scripps Institution of Oceanography, and
Corine Glé
Scripps Institution of Oceanography, and
Aaron C. Hartmann
Scripps Institution of Oceanography, and
Mark Hildebrand
Scripps Institution of Oceanography, and
William H. Gerwick1 [email protected]
Scripps Institution of Oceanography, and
Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA 92093

Notes

1
To whom correspondence should be addressed. E-mail: [email protected].
Author contributions: E.M.T., R.P.S., M.H., and W.H.G. designed research; E.M.T., S.R.S., C.G., and A.C.H. performed research; S.R.S. contributed data and technical support; E.M.T., C.G., A.C.H., M.H., and W.H.G. analyzed data; M.H. and W.H.G. provided technical support; and E.M.T. wrote the paper.

Competing Interests

The authors declare no conflict of interest.

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    Metabolic engineering of lipid catabolism increases microalgal lipid accumulation without compromising growth
    Proceedings of the National Academy of Sciences
    • Vol. 110
    • No. 49
    • pp. 19653-19969

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