Brookhaven research associates Jilian Fan, Changcheng Xu and Chengshi Yan analysing cultures of algae. (Photo: BNL)
Carbon availability vital to oil biosynthesis in algae: study
Tuesday, June 19, 2012, 22:40 (GMT + 9)
Scientists at the US Department of Energy’s Brookhaven National Laboratory (BNL) have countered two long-held misconceptions about oil production in algae as they showed that ramping up the microbes’ overall metabolism by feeding them more carbon increases oil production as the organisms continue to grow.
Before the Brookhaven research, a main approach to optimizing oil production in algae was to starve the algae of certain key nutrients, such as nitrogen. Oil output would increase, but the algae would stop growing—not an ideal outcome for continuous production.
The findings—published online in the journal Plant and Cell Physiology—may point to new ways to use photosynthetic green algae for the production of algal oils for alternative fuels.
|Confocal image of the algae Chlamydomonas showing the accumulation of oil droplets (golden dots). Red represents chlorophyll autofluorescence. (Photo: BNL)
“Much of what we thought we knew was inferred from studies performed on higher plants,” said Brookhaven biochemist John Shanklin, a co-author who’s conducted extensive research on plant oil production. Recent studies have hinted at big differences between the microbial algae and their more complex photosynthetic relatives.
The Brookhaven scientists grew cultures of Chlamydomonas reinhardtii under a variety of nutrient conditions, with and without inhibitors that would limit specific biochemical pathways. They also studied a mutant Chlamydomonas that lacks the capacity to make starch.
By comparing how much oil accumulated over time in the two strains across the various conditions, they were able to learn why carbon preferentially partitions into starch rather than oil, and how to affect the process.
The main finding was that feeding the algae more carbon (in the form of acetate) quickly maxed out the production of starch to the point that any additional carbon was channeled into high-gear oil production. And, most significantly, under the excess carbon condition and without nutrient deprivation, the microbes kept growing while producing oil.
The detailed studies, conducted mainly by Brookhaven research associates Jilian Fan and Chengshi Yan, showed that the amount of carbon was the key factor determining how much oil was produced: more carbon resulted in more oil; less carbon limited production.
This is an example of a substantial difference between algae and higher plants, said co-author John Shanklin. In plants, the enzymes directly involved in the oil biosynthetic pathway are the limiting factors in oil production. In algae, the limiting step is not in the oil biosynthesis itself, but further back in central metabolism.
The next step for the Brookhaven team will be to look more closely at the differences in carbon partitioning in algae and plants. This part of the work will be led by co-author Jorg Schwender, an expert in metabolic flux studies.
The team will also work to translate what they’ve learned in a model algal species into information that can help increase the yield of commercial algal strains for the production of raw materials for biofuels.
This research was funded by the DOE Office of Science and the DOE Office of Energy Efficiency and Renewable Energy.