Sandia National Laboratories scientists Seema Singh, left; and Fang Liu hold vials of vanillin and fermentation broth, which are critical for turning plant matter into biofuels and other valuable chemicals. Credit: Dino Vournas

While it has long been known that plant matter has the potential to produce renewable fuels, doing so efficiently and inexpensively has turned out to be a difficult roadblock to overcome.

However, E. coli—bioengineered by scientists from Sandia National Laboratories—could make it economically feasible to produce jet fuel, as well as other materials like plastics, nylon, pharmaceuticals and other products from lignin, an organic polymer that helps form the tissues of vascular plants.

Sandia bioengineer Seema Singh said in an interview with R&D Magazine that the new process could be a boon for industries looking for cheaper renewable fuels.

“This will enable a lot of self-sustainability because these are greener renewable fuels,” Singh said. “It will also create a lot of domestic jobs. The main reason most of the early bioscience projects have failed has been about the cost of the fuel is not cost competitive.”

According to Singh, the researchers applied their understanding of natural lignin degraders to the bioengineered bacteria. E. coli grows fast and can survive the harsh industrial processes needed to produce the platform chemicals needed to create green fuels.

Lignin is the component of plant cell walls that gives them their incredible strength. Lignin is also brimming with energy and, once broken down to the form of platform chemicals, can be converted into nylon, plastics, pharmaceuticals and other products.

“The lignin is a really, really tough polymer and the reason that it is difficult is because the function of the lignin in the plant is to provide the plant to have some mechanism of protecting it,” she added.

E. coli typically does not produce the enzymes required for the conversion process. However, the researchers coaxed the bacteria into making enzymes by adding an inducer to the fermentation broth.

While inducers are generally expensive to use, the researchers were able to circumvent the cost of the inducer by engineering the bacteria so that lignin-derived compounds like vanillin can serve as both the substrate and the inducer.

While the researchers—which included Singh and two postdoctoral researchers, Weihua Wu, now at Lodo Therapeutics Corp., and Fang Liu—were able to clear the cost hurdle using vanillin, they still had issues due to toxicity and a lack of efficiency.

While vanillin is produced as lignin breaks down, it can inhibit the E. coli at higher concentrations, posing a potential toxicity problem. To get around this issue, the researchers initiated a complex process called lignin valorization that causes the vanillin to activate the enzyme in the fermentation broth. The E. coli then starts to convert the vanillin into catechol—the desired chemical—preventing the amount of vanillin to reach a toxic level.

“It will never reach to the high levels of concentration because it is constantly being utilized,” Singh said. “It never reaches the concentration where it becomes toxic.”

While the vanillin in the fermentation broth moved across the membranes of the cells to be converted by the enzymes, it does so in a slow and passive movement. To improve the efficiency of the process, the researchers looked for effective transporters from other bacteria and microbes and used a transporter design from another microbe and engineered it into the E. coli. This helps pump the vanillin in to the bacteria.

Next, the researchers plan to demonstrate that they can produce more chemicals using their new method, as well as producing a larger yield of chemicals produced.