Feeding Sugars to Algae Makes Them Fat

March 1, 2019

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Cryo-soft X-ray tomography of an algal cell shows the large accumulation of fat (yellow). Nucleus, purple; chloroplast, green; mitochondria, red; lipid bodies, yellow.
Cryo-soft X-ray tomography of an algal cell shows the large accumulation of fat (yellow). Nucleus, purple; chloroplast, green; mitochondria, red; lipid bodies, yellow.
Image courtesy of Melissa Roth, University of California, Berkeley, and Andreas Walter, Lawrence Berkeley National Laboratory

The Science

Algae can make dramatic shifts in their metabolism in response to changes in their environment. Some microscopic green algae stop photosynthesizing and start accumulating fats and/or other valuable molecules when certain changes happen. However, scientists don’t know the details of those swift metabolic changes. A team examined a green microalga to better understand this process. After a few days of feeding this microbe sugar, it completely dismantles its photosynthetic apparatus while accumulating fat. In contrast, after the team stopped feeding it sugar, the microbe returned to its normal metabolism.

The Impact

Algae could be a sustainable source of biofuels and other valuable chemicals. As they trap carbon dioxide from the air by photosynthesis, they convert greenhouse gases into oils and other useful industrial products. Scientists need to know how algae control their metabolism to engineer strains that can make desirable products. This study showed that feeding glucose (sugar) to this alga affects one-third of its genes. This extensive catalog of affected genes opens the door to identify and manipulate critical genes that will dramatically increase oil production along with other tailored bioproducts.

Summary

Microalgae can produce large quantities of valuable oils and other chemicals, but their tight metabolic regulation poses a challenge to engineer these organisms for industrial-level production of biofuels and bioproducts. Using a variety of imaging and genomics technologies, a team from the University of California and national labs determined that only a few days after adding glucose to a culture of the green alga Chromochloris zofingiensis growing in the light, algal cells accumulate large amounts of the biofuel precursors triacylglycerols as well as economically important products, such as carotenoids. Further, they observed that photosynthesis shut off and the photosynthetic apparatus disappeared, while the overall culture biomass increased. At the same time, nearly one-third of the genes in the genome changed their expression during these growth and metabolic alterations. The researchers also discovered that these changes were readily reversed when they removed the glucose from the culture. Elucidation of the pathways that lead to high accumulation of those biofuels and bioproducts will allow scientists to engineer algae as sustainable biofactories.

Contact

Program Manager

Pablo Rabinowicz
Office of Biological and Environmental Research, Office of Science, Department of Energy 
pablo.rabinowicz@science.doe.gov

Principal Investigators

Melissa Roth
University of California, Berkeley
melissa.s.roth@gmail.com

Krishna K. Niyogi
University of California, Berkeley
niyogi@berkeley.edu
 

Funding

This research was supported by the Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research. The authors acknowledge work performed by the DOE Joint Genome Institute (a DOE Office of Science user facility), the DOE Joint BioEnergy Institute, and the National Center for X-ray Tomography. The cryo-soft X-ray tomography was supported by the Photosynthetic Systems program in the DOE, Office of Science, Office of Basic Energy Sciences. The authors also acknowledge funding and support from the U.S. Department of Agriculture National Institute of Food and Agriculture, the National Institutes of Health, the National Science Foundation, and the Howard Hughes Medical Institute. 

Publications

M.S. Roth, S.D. Gallaher, D.J. Westcott, et al.,Regulation of oxygenic photosynthesis during trophic transitions in the green alga Chromochloris zofingiensis.” The Plant Cell (2019). [DOI: 10.1105/tpc.18.00742]

Related Links

University of California, Los Angeles news release: Discovery of an alga’s ‘dictionary of genes’ could lead to advances in biofuels, medicine