A team of scientists from Washington University has discovered a new way to use microbes to produce readily usable biofuel. It involves genetically modifying a bacteria called Rhodopseudomonas palustris TIE-1 so that it will produce biofuel using only carbon dioxide, solar panel-generated electricity, and light.
The process designed by the Washington research team resulted in a biofuel called n-butanol, a carbon-neutral fuel alternative that they say can be mixed with diesel or gasoline.
Background: Finding the right microbe
The world has entered the race to become climate-neutral with net-zero greenhouse emissions. Combating the catastrophic use of fossil fuels and CO2 emissions is a priority, and several companies and researchers are looking for innovative ways to join the battle.
Previous studies have used microbes to produce sustainable biofuels, however, most results were deemed as inefficient. It’s common for bacteria to produce secondary compounds that have an inactivation effect on the pathways involved with the biosynthetic pathways, which leads to a decrease in overall production.
Rhodopseudomonas palustris, however, is different from the other “contestants”. For the research team, it was an obvious choice: “We chose it because it interacts well with electricity and due to its many different metabolic modes”, Arpita Bose, associate professor of Biology in Arts & Sciences at Washington University, and leader of the study told The Debrief. “Most other microbes don’t display this level of metabolic diversity”.
Analysis: Creating microbial fuel
The research team set out to explore how the TIE-1 strain of the bacteria could be exploited to produce biofuel. They created a mutant version of the microbe that could not fix nitrogen and introduced an artificial n-butanol biosynthesis pathway into it.
“The fuel we made, n-butanol, has a high energy content and low tendency to vaporize or dissolve in water without combustion,” Wei Bai, a Ph.D. graduate of McKelvey Engineering’s Department of Energy, Environmental & Chemical Engineering, said. “This is especially true when compared with ethanol, which is a commonly used biofuel.”
These microbes were “fed” using solar panel-generated electricity, through a technique called microbial electrosynthesis (MES). Inside a specific reactor, the bacteria attach themselves to a negative charge and begin to “eat” electricity.
“Microorganisms have evolved a bewildering array of techniques to obtain nutrients from their surrounding environments,” Bose said. “Perhaps one of the most fascinating of these feeding techniques uses microbial electrosynthesis (MES). Here we have harnessed the power of microbes to convert carbon dioxide into value-added multi-carbon compounds in a usable biofuel.”
The n-butanol produced by the modified bacteria presented great benefits as a drop-in fuel, meaning that this renewable fuel easily blends with petroleum products, like gasoline and diesel, and it’s usable in the current infrastructure of pumps, pipelines, and other existing equipment. “The fuel we made, n-butanol, has a high energy content and low tendency to vaporize or dissolve in water without combustion,” Bai said. “This is especially true when compared with ethanol, which is a commonly used biofuel.”
Outlook: The future is bright… and microscopic
When questioned about the costs of mass-producing n-butanol through this process, Bose told The Debrief that, while cost analysis is underway, “TIE-1 uses cheap carbon dioxide, so you can see how the low feedstock cost would lower production costs when we compare these microbes to those that need organic carbon”.
There’s also the question of sustainability. Bose mentioned that “Industrial-scale manufacturing of bioplastics and biofuels using microbial electrosynthesis can be achieved using the electricity produced by solar panels, creating a fully sustainable cycle”. For now, as Bose told The Debrief, they are still looking into determining what areas of the process may not be sustainable, to improve them in the future.
Several companies are producing n-butanol as biofuel at the moment. Bose considers that, in order to mass-produce n-butanol using the process that she and her team developed, the best way would be to “co-opt existing mass-production approaches and facilities”.
The more knowledge scientists gather from these modified microbes, the more potential they see in them. “To the best of our knowledge, this study represents the first attempt for biofuel production using a solar panel-powered microbial electrosynthesis platform, where carbon dioxide is directly converted to liquid fuel,” Bai said. “We hope that it can be a stepping stone for future sustainable solar fuel production.”
“The United States and the European Union recognize microbial electrosynthesis as a key technology for sustainability and climate change solutions,” Bose said. “Ultimately, by exploiting a microbial metabolism that evolved in the distant past, we hope that new methods will emerge to help address some of the most pressing problems of our time.”
So far, the n-butanol created by the bacteria engineered by Bose’s team can only be used as a drop-in fuel for conventional vehicles. However, Bose told The Debrief that the team is already working on new techniques that could result in the creation of new biofuels that could completely substitute the fossil fuels that we currently use.