esearchers at Iowa State University, in Ames, IA, are exploring the effects of controlling the expression of two algal genes that regulate the uptake of CO2 for photosynthesis. In the experiments performed under the direction of Martin Spalding, professor in the Department of Genetics, Development, and Cell Biology, the researchers noticed an increase in the algal biomass by 50 to 80 percent when these two genes were artificially expressed.
“The key to this (increase in biomass) is a combination of two genes that increase the photosynthetic carbon conversion into organic matter by 50 percent over the wild type under carbon dioxide enrichment conditions,” said Dr. Spalding.
In environments that have relatively low levels of CO2, two genes in algae—LCIA and LCIB—are expressed, or turned on, to help capture and then channel more carbon dioxide from the air into the cells to keep the algae alive and growing. However, when algae are in environments with high carbon dioxide levels, such as in soil near plant roots that are expiring carbon dioxide, the two relevant genes shut down because the plant is getting enough carbon dioxide.
“The process is similar to a car driving up a hill,” says Spalding. “The accelerator—these two genes—is pressed and the engine works hard to climb a hill. But when going down an incline, the driver often lets up on the accelerator since more gas isn’t needed—the genes shut down. The two genes are expressed—essentially keeping algae’s foot on the gas—even when they are in a carbon dioxide-rich environment and don’t need additional carbon dioxide.”
In experiments to get the algae type (Chlamydomonas reinhardtii) to produce more biomass, Spalding first expressed LCIA and LCIB separately. Each indicated a 10 to 15 percent increase in biomass. When the two genes were expressed together, researchers were surprised to see the 50 to 80 percent biomass increase. “Somehow these two genes are working together to increase the amount of carbon dioxide that’s converted through photosynthesis into biomass by the algae under conditions where you would expect there would already be enough carbon dioxide,” said Spalding.
This research was funded in part by grants from the Department of Agriculture’s National Institute of Food and Agriculture and the Department of Energy, Advanced Research Projects Agency—Energy.