Our greatest chance to win the biofuels bet is now called Nannochloropsis gaditana. These marine micro-algae do not need fresh water and produce large amounts of fat easy to convert into biodiesel. But even the best natural talent must be cultivated with hard work. Imad Ajjawi and colleagues did just that in the lab, doubling the lipid content of their algae with the help of CRISPR, the celebrated gene-editing technique.
The exploit has been published in Nature Biotechnology by scientists from Synthetic Genomics, the company founded by the human genome cracker Craig Venter, partnering with ExxonMobil. In the global warming era, algae are a tempting option because they actively consume carbon dioxide, without competing for arable lands with food production. The quest for the perfect algae in nature, however, has proven more difficult than hoped for. Natural metabolism must be optimized for lipid production to achieve economic besides environmental sustainability. Algae, in short, must be induced to produce more fat than they would need in normal conditions. Such a goal can be achieved by starving them of a nutrient essential for protein synthesis (nitrogen) but at the price of hindering photosynthesis and growth. An alternative is to tinker algal metabolism by genetic engineering, but this path has been slowed down by technical difficulties until the invention of CRISPR. This revolutionary genetic modification system has now been adapted to Nannochloropsis gaditana and used to identify genetic changes triggered by nitrogen deficiency. Some 20 candidate genes were selected and disrupted one by one to study their role. Researchers knew they were on the right track when, knocking out the ZnCys gene, growth slowed down, but lipid content tripled. The next step was fine-tuning, by lowering instead than silencing gene expression. The result is a strain with about 40 percent of its mass as fat, more than doubling the figure of wild-type algae, without significantly inhibiting growth. That’s a real breakthrough, but commercial applications are still decades away. Several pieces of the scientific puzzle are still missing, and outdoors production will require approval from regulators.
(photo credit: Synthetic Genomics)