Creating Plastics from Electricity with “Biobatteries”

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed. With the expansion of renewable electricity sources worldwide, which harvest energy from natural sources such as sunlight, steam, and currents, the energy sector is uncovering a new challenging question: how do we store excess electricity? The world has a relative shortage of storage capacity for these renewables. Meanwhile, our current industries use petroleum to create energy, fuel, and plastics as well. However, petroleum is a resource that releases fossilized carbon from the ground into the atmosphere when utilized, contributing significantly to the climate crisis..

WashU biologist Arpita Bose is researching natural, sustainable solutions to our unnatural, disastrous problems. The solution, she believes, requires us to look back to life’s roots. As written on her lab’s research page, “First things first — this is a microbial world.” She believes that biology, the staple of sustainable Earth systems, can connect the dots between our newfound excess electrical energy and our destructive dependence on petrochemicals for energy and plastics. 

In her quest for answers, Bose researches Rhodopseudomonas palustris TIE-1 and its cousins. This microbe has a metabolism that the Bose lab believes has potential for fundamental economic change. Energized by sunlight, these autotrophs can sustain themselves on carbon dioxide from the atmosphere and electrons from charged electrodes. The organism electrosynthesizes the components into biomass and a biodegradable plastic called polyhydroxybutyrate. Essentially, TIE-1 can clean our air by producing bioplastics if given access to sunlight and electricity. This complements the new surpluses generated by renewables, for TIE-1 acts as a “biobattery”.

Both plants and TIE-1 are photosynthetic, meaning they use solar energy to energize electrons and reduce carbon dioxide. The key difference between a plant’s photosystem and that of TIE-1 is where they source their electrons. Whereas plants use water to supply a stable source of electrons to reduce carbon dioxide, these microbes use charged electrodes. Bose compares its metabolism to a “biobattery” because you can “charge” them to generate biodegradable plastics.

Even more optimistically, Bose can make changes to the DNA of TIE-1 to produce other desired outcomes. She can engineer these microbes to produce not just bioplastics, but potentially other valuable materials. For instance, with more research, she is hopeful that her lab may help discover new strategies to make “electrofuels”: biofuels produced using electricity.

Bose notes that the research has not yet enabled the production of bioplastics to supersede the economic superiority of petroleum products. People will continue using what they have, for the systems and infrastructure are already in place. However, she believes that in order to find truly sustainable solutions, we must embrace biology in our economy. Not only are biological systems the essence of life on Earth, but if we study them we don’t have to reinvent the wheel. Evolution has already done much of the work for us. As Bose puts it, “[biology presents] infinite possibilities. Nature contains amazing answers. In this case, the answers may lie in the soil beneath our very feet.”

Relevant Publications:

Ranaivoarisoa, T.O., Singh, R., Rengasamy, K. et al. Towards sustainable bioplastic production using the photoautotrophic bacterium Rhodopseudomonas palustris TIE-1. J Ind Microbiol Biotechnol 46, 1401–1417 (2019). https://doi.org/10.1007/s10295-019-02165-7.

Karthikeyan, R., Singh, R. & Bose, A. Microbial electron uptake in microbial electrosynthesis: a mini-review. J Ind Microbiol Biotechnol 46, 1419–1426 (2019). https://doi.org/10.1007/s10295-019-02166-6.

Singh R., Ranaivoarisoa T.O., Gupta D. et al. Genetic Redundancy in Iron and Manganese Transport in the Metabolically Versatile Bacterium Rhodopseudomonas palustris TIE-1. Applied and Environmental Microbiology, Aug 2020, 86 (16) e01057-20. https://doi.org/10.1128/AEM.01057-20.

Gupta D., Sutherland, M.C., Rengasamy K. et al. Photoferrotrophs Produce a PioAB Electron Conduit for Extracellular Electron Uptake. mBio Nov 2019, 10 (6) e02668-19. https://doi.org/10.1128/mBio.02668-19.
Guzman, M.S., Rengasamy, K., Binkley, M.M. et al. Phototrophic extracellular electron uptake is linked to carbon dioxide fixation in the bacterium Rhodopseudomonas palustris. Nat Commun 10, 1355 (2019). https://doi.org/10.1038/s41467-019-09377-6.