In earlier work, the UT Austin team had already enhanced lipogenesis titers in Y. lipolytica using rational metabolic engineering efforts. However, they found that the resulting strain still suffered from decreased biomass generation rates. In the new study, they used a rapid evolutionary metabolic engineering approach linked with a floating cell enrichment process to improve lipogenesis rates, titers, and yields.

Through this iterative process, we were able to ultimately improve yields from our prior strain by 55% to achieve production titers of 39.1 g/L with upwards of 76% of the theoretical maximum yield of conversation. Isolated cells were saturated with up to 87% lipid content. An average specific productivity of 0.56 g/L/h was achieved with a maximum instantaneous specific productivity of 0.89 g/L/h during the lipid production phase in fermentation.

—Liu et al.

The strain’s high lipid yield makes it one of the most efficient organisms for turning sugar into lipids. In addition, the resulting cells produced these lipids at a rate that was more than 2.5 times as fast as the previous strain.

The new yeast developed by Hal Alper, associate professor in the McKetta Department of Chemical Engineering, and his team aligns with the US Department of Energy’s efforts to develop renewable and cost-competitive biofuels from nonfood biomass materials.

This significant improvement in our cell-based platform enables these cells to compete in the biofuels industry. We have moved to concentration values that begin to align with those in other industrial fuel processes.

—Hal Alper

Alper and his team improved the performance of Yarrowia through a combination of metabolic engineering and directed evolution, which, like the process of natural selection, seeks to identify and cultivate the high-performing cells. In this work, the researchers recognized that cells with high lipid content would float to the top of a tube, whereas cells with lower lipid content would settle down to the bottom. The researchers used this “floating cell scheme” to identify the best-performing cells.

The researchers used these high-performing cells, cells that produced more lipids and at a faster rate, to obtain the final yeast with improved function.

The researchers’ method and platform are patent pending. Alper’s lab is continuing to work on ways to improve how the yeast strain converts sugar into lipids, and on the types of lipid products they can produce.

This research received funding from the Office of Naval Research Young Investigator Program, the DuPont Young Investigator Award and the Welch Foundation.

Resources

• Leqian Liu, Anny Pan, Caitlin Spofford, Nijia Zhou, Hal S. Alper (2015) “An evolutionary metabolic engineering approach for enhancing lipogenesis in Yarrowia lipolytica,” Metabolic Engineering, Volume 29, Pages 36-45 doi: 10.1016/j.ymben.2015.02.003