Researchers at Synthetic Genomics’ laboratory discovered a new process for increasing oil production by identifying a genetic switch that could be fine-tuned to regulate the conversion of carbon to oil in the algae species, Nannochloropsis gaditana. The team established a proof-of-concept approach that resulted in the algae doubling its lipid fraction of cellular carbon compared to the parent—while sustaining growth.

Despite decades of research, previous genetic-engineering approaches have failed to yield substantial improvements in lipid productivity for any Nannochloropsis species. A lack of efficient genome-editing tools for industrially relevant strains and an inability to increase lipid productivity without decreasing growth rate have confounded efforts to engineer this genus.

Here, we report a high-efficiency CRISPR–Cas9 reverse-genetics pipeline for N. gaditana (CCMP1894), which we applied to identify a transcriptional regulator of lipid accumulation, Zn(ii)2Cys6 (ZnCys). Modulation of ZnCys expression enabled us to double the strain’s lipid productivity while retaining its ability to grow and fix CO₂ at levels nearly equivalent to those of the wild type (WT) strain under dense semicontinuous culture.

… Our findings represent a step toward understanding and controlling lipid production in algae. This ability to control algal lipid production might eventually enable the commercialization of microalgal-derived biofuels.

—Ajjawi et al.

Algae has been regarded as a potential sustainable fuel option, but researchers have been hindered for the past decade in developing a strain that is high in oil content and grows quickly—two critical characteristics for scalable and cost-efficient oil production. Slower growth has been an adverse effect of previous attempts to increase algae oil production volume.

A key objective of the ExxonMobil-Synthetic Genomics collaboration has been to increase the lipid content of algae while decreasing the starch and protein components without inhibiting the algae’s growth. Limiting availability of nutrients such as nitrogen is one way to increase oil production in algae, but it can also significantly inhibit or even stop photosynthesis, stunting algae growth and ultimately the volume of oil produced.

The ability to sustain growth while increasing oil content is an important advance. Algae has other advantages over traditional biofuels because it can grow in salt water and thrive in harsh environmental conditions, therefore limiting stress on food and fresh water supplies.

Oil from algae can also potentially be processed in conventional refineries, producing fuels no different from convenient, energy-dense diesel. Oil produced from algae also holds promise as a potential feedstock for chemical manufacturing.

The SGI-ExxonMobil science teams have made significant advances over the last several years in efforts to optimize lipid production in algae. This important publication today is evidence of this work, and we remain convinced that synthetic biology holds crucial answers to unlocking the potential of algae as a renewable energy source. We look forward to continued work with ExxonMobil so that eventually we will indeed have a viable alternative energy source.

—J. Craig Venter, Ph.D., Synthetic Genomics co-founder and chairman

Since 2009, ExxonMobil and Synthetic Genomics have been partners in researching and developing oil from algae to be used as a renewable, lower-emission alternative to traditional transportation fuels. Swarup said that while the breakthrough is an important step, the technology is still many years from potentially reaching the commercial market.

This key milestone in our advanced biofuels program confirms our belief that algae can be incredibly productive as a renewable energy source with a corresponding positive contribution to our environment. Our work with Synthetic Genomics continues to be an important part of our broader research into lower-emission technologies to reduce the risk of climate change.

Advancements as potentially important as this require significant time and effort, as is the case with any research and development project. Each phase of our algae research, or any other similar project in the area of advanced biofuels, requires testing and analysis to confirm that we’re proceeding down a path toward scale and commercial viability.

—Vijay Swarup, vice president for research and development at ExxonMobil Research and Engineering Company

ExxonMobil is engaged in a wide range of research on advanced biofuels, partnering with universities, government laboratories, and other companies. Global demand for transportation-related energy is projected to increase by about 25% through 2040, and accelerating the reduction in emissions from the transportation sector will play a critical role in reducing global greenhouse gas emissions.

ExxonMobil is also actively researching other emission-reducing technologies, including carbon capture and sequestration. In 2016, ExxonMobil announced its partnership with Connecticut-based FuelCell Energy, Inc. to advance the use of carbonate fuel cells to economically capture carbon emissions from power plants while generating hydrogen and additional electricity. Since 2000, ExxonMobil has spent about $8 billion to develop and deploy lower-emission energy solutions across its operations.

Resources

• Imad Ajjawi, John Verruto, Moena Aqui, Leah B Soriaga, Jennifer Coppersmith, Kathleen Kwok Luke Peach, Elizabeth Orchard, Ryan Kalb, Weidong Xu, Tom J Carlson, Kristie Francis, Katie Konigsfeld, Judit Bartalis, Andrew Schultz, William Lambert, Ariel S Schwartz, Robert Brown, Eric R Moellering (2017) “Lipid production in Nannochloropsis gaditana is doubled by decreasing expression of a single transcriptional regulator” Nature Biotechnology doi: 10.1038/nbt.3865