Researchers at Washington University in St. Louis have discovered a new way to train microbes to make n-butanol. A team of biologists and engineers modified Rhodopseudomonas palustris TIE-1 (TIE-1) so that it can produce a biofuel using only three renewable and naturally abundant source ingredients: carbon dioxide, solar panel-generated electricity and light.

The resulting biofuel, n-butanol, is a carbon-neutral fuel alternative that can be used in blends with diesel or gasoline. The results are reported in an open-access paper in the journal Communications Biology.

Microorganisms have evolved a bewildering array of techniques to obtain nutrients from their surrounding environments. 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.

—Arpita Bose, associate professor of biology in Arts & Sciences, and leader of the study

The first author of the study is Wei Bai, a PhD graduate of McKelvey Engineering’s Department of Energy, Environmental & Chemical Engineering. Bai worked as a research assistant in the Bose lab in Arts & Sciences from 2015-2020. Bai is now a scientist at Amyris, a manufacturer of sustainable ingredients made with synthetic biology.

Microbes that feed through microbial electrosynthesis attach themselves directly to a negatively charged cathode inside the MES reactor so that they can “eat” electricity. Previous research from the Bose lab helped illuminate how microbes such as TIE-1 use electrons to fix carbon dioxide and also how they can be used to create sustainable bioplastics.

As scientists learn more about these microbes, their potential uses are more and more promising, Bose said, though she acknowledged that improvements are needed before the techniques can be rolled out on industrial scales.

Other researchers previously have explored the use of microbes such as cyanobacteria to produce sustainable biofuels. However, these types of organisms produce oxygen during photosynthesis, which tends to limit their efficiency for synthesizing biofuels, as many of the enzymes involved in the biosynthetic pathways are oxygen-sensitive.

To explore how TIE-1 could be exploited to produce biofuel, Bai and Bose constructed a mutant form of the microbe that could not fix nitrogen. The scientists then introduced an artificial n-butanol biosynthesis pathway into this new mutant.

The form of the microbe they built was unable to grow when nitrogen gas was its only nitrogen source. So instead, this version of TIE-1 channeled its effort into producing n-butanol—increasing its yield of biofuel without increasing electricity consumption significantly.

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. We hope that it can be a steppingstone for future sustainable solar fuel production.

—Wei Bai

Resources

• Bai, W., Ranaivoarisoa, T.O., Singh, R. et al. (2021) “n-Butanol production by Rhodopseudomonas palustris TIE-1.” Commun Biol 4, 1257 doi: 10.1038/s42003-021-02781-z