Donald Danforth Plant Science Center associate member Dr. James Umen and his colleagues have discovered a way to make algae better at producing oil, such as for biofuels, without sacrificing growth.
Umen's team included lead author Dr. Inmaculada Couso and collaborators Dr. Bradley Evans, director of Proteomics & Mass Spectrometry, and Dr. Doug Allen, U.S. Department of Agriculture research scientist at the Danforth Center. They identified a mutation in the green alga Chlamydomonas that substantially removes a widely observed constraint in micro-algae in which the highest yields of oil can be obtained only from starving cultures.
The findings were published last month in The Plant Cell in a paper titled "Synergism Between Inositol Polyphosphates & TOR Kinase Signaling in Nutrient Sensing, Growth Control & Lipid Metabolism in Chlamydomonas."
Umen and his team found vip1-1, an oil-accumulating mutation in Chlamydomonas, while investigating how two conserved signaling systems interact with one another.
One system involves a protein called TOR (target of rapamycin), whose activity is tuned to match the cell growth rate with nutrient levels in the environment.
The other system involves a family of proteins called VIP that produce highly phosphosphorylated small molecules called inositol polyphosphates that are thought to act as intracellular signals but whose function in algae is not well defined. The team found that when VIP activity was reduced by the vip1-1 mutation, cell growth became extremely sensitized to changes in TOR activity, but unexpectedly, this sensitivity was dependent on the sources of carbon nutrients the cells had available.
When TOR-inhibited vip1-1 cells were given light for photosynthesis and supplemented with acetate — a "free" source of extra carbon — their growth was completely arrested. However, the vip1-1 mutation had no impact on TOR-inhibited cell growth when acetate was removed and atmospheric carbon dioxide was the only source of carbon.
The connection between acetate and the growth behavior of vip1-1 cells led the team to investigate the mutation further to see if it had other metabolic alterations that could be detected without perturbing TOR signaling.
Remarkably, they found that actively growing vip1 cells were oil over-accumulators that made extra storage oil compared to normal cells, and did so without incurring a significant growth penalty. Moreover, during starvation conditions when normal cells boost their oil content significantly, vip1-1 cells increased it even more, with up to double the yields seen in normal cells.
"Our study reveals a new way to understand how cells control carbon metabolism and storage," said Couso, a post-doctoral researcher at Institute of Plant Biochemistry & Photosynthesis. "As we decipher the inositol polyphosphate signaling code, we open up the prospect of being able to reprogram metabolism and make algae better producers of oil or other high-value, carbon-rich compounds."
Founded in 1998, the Donald Danforth Plant Science Center is a not-for-profit research institute with a mission to improve the human condition through plant science. The center's research, education and outreach aim to have an impact at the nexus of food security and the environment. Its work is funded through competitive grants from many sources, including the National Institutes of Health, U.S. Department of Energy, National Science Foundation and Bill & Melinda Gates Foundation.