Whilst the ability to produce fuels from renewable, organic matter has long been known, chemists are still unable to manufacture higher performance fuels, such as diesel, in an economically feasible way. This is a major problem for the biofuel industry and a global challenge for a world where so many goods sent via diesel engines on trucks and ships have an impact on climate change.
But now bio-engineers may be closer to solving this problem as they have genetically engineered a strain of yeast to convert sugars from organic matter to fats more effectively. While the breakthrough has only increased the process’s efficiency by 30%, it is thought that the research could be a breakthrough to making production of better performing biofuels, including bio-diesel, economically viable.
As professor Gregory Stephanopoulos, the Willard Henry Dow Professor of Chemical Engineering and Biotechnology, and one of the lead reseachers in the study conducted at MIT, notes, “Diesel is the preferred fuel because of its high energy density and the high efficiency of the engines that run on diesel. The problem with diesel is that so far it is entirely made from fossil fuels.”
The technical issue, according to the study published in the journal Nature Biotechnology, is that, “While microbial factories have been engineered to produce lipids from carbohydrate feedstocks for production of biofuels and oleochemicals, even the best yields obtained to date are insufficient for commercial lipid production.”
While there has been a lot of success in converting cooking oil to biofuel, this feedstock is in relatively short supply. More readily available biofuel feedstock, such as corn and sugar cane, requires converting carbohydrates into lipids, before they can be made into a fuel. The fact that this process is uneconomical when compared to fossil fuels, led the MiT team to look at ways of improving the efficiency of the process. They hope to be able to use cheaper and more abundant organic feedstock to make biodiesel.
The website MiT News explained the achievement as follows, “Stephanopoulos and his colleagues [including fellow leader, MIT postdoc, Kangjian Qiao] began working with a yeast known as Yarrowia lipolytica, which naturally produces large quantities of lipids. They focused on fully utilizing the electrons generated from the breakdown of glucose. To achieve this, they transformed Yarrowia with synthetic pathways that convert surplus NADH, a product of glucose breakdown, to NADPH, which can be used to synthesize lipids. Using this improved pathway, the yeast cells require only two-thirds of the amount of glucose needed by unmodified yeast cells to produce the same amount of oil.”
“It turned out that the combination of two of these pathways gave us the best results that we report in the paper,” Stephanopoulos said. Although the team also admits that, “The actual mechanism of why a couple of these pathways work much better than the others is not well-understood.”
So clearly there is still much work to do before renewable diesel is powering trucks on our highways. However, the researchers are continuing their work, funded by the U.S. Dept of Energy, with the ultimate aim of being able to use not just sugar cane and corn starch, but any, “plant material, such as grass and agricultural waste. [Although this] would require converting the cellulose that makes up those plant materials into glucose.”
As Stephanopoulos says, “There is still room for more improvement, and if we push more in this direction, then the process will become even more efficient, requiring even less glucose to produce a gallon of oil. What we’ve done is reach about 75% of this yeast’s potential, and there is an additional 25% that will be subject of follow-up work.”
When and exactly how this last 25% of the goal will be met is unknown, but biotechnology engineers and biofuel manufacturers are keeping a close eye on progress. With governments keen to lower their carbon footprint and dependency on oil, then the work being carried out at MiT could see a renewable biodiesel, at an economically viable process, much sooner than we think.