In Missouri, James Umen, Ph.D., associate member at Donald Danforth Plant Science Center, and colleagues have discovered a way to make algae better oil producers without sacrificing growth.
Umen and his team found the oil-accumulating mutation in Chlamydomonas, called vip1-1, 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 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 that 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 CO2 was the only carbon source.
The findings were published September 6, in a paper titled, “Synergism between inositol polyphosphates and TOR kinase signaling in nutrient sensing, growth control and lipid metabolism in Chlamydomonas,” in The Plant Cell. Umen and his team including lead author Inmaculada Couso, Ph.D., and collaborators Bradley Evans Ph.D., director, Proteomics & Mass Spectrometry and Doug Allen, Ph.D., USDA Research Scientist at the Danforth Center identified a mutation in the green alga Chlamydomonas which substantially removes a constraint that is widely observed in micro-algae where the highest yields of oil can only be obtained from starving cultures.