Engineered Microbes Offer Potential Energy Storage Solution

May 28, 2019 by Scott McMahan

Engineered electroactive microbes could be part of an energy storage solution for intermittent renewable power sources, according to research conducted at Cornell University.

These microbes can borrow an electron from solar or wind electricity, and then use this energy to break apart carbon dioxide molecules from the air. The microbes could then take the carbon atoms to produce biofuels, including propanol or isobutanol, that can be burned added to gasoline or burned in a generator, for example.

"We think biology plays a significant role in creating a sustainable energy infrastructure," said Buz Barstow, assistant professor of biological and environmental engineering. "Some roles will be supporting roles and some will be major roles, and we're trying to find all of those places where biology can work."

In theory, adding electrically engineered (synthetic or non-biological) elements in this process could make the approach more productive and efficient than microbes alone.

Also, having many options can create too many engineering choices. The study supplies information that can help determine the best design based on particular needs.

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"We are suggesting a new approach where we stitch together biological and non-biological electrochemical engineering to create a new method to store energy," said Farshid Salimijazi, a graduate student in Barstow's lab and the paper's first author.

Natural photosynthesis can already store solar energy at a huge scale and turn it into biofuels in a closed carbon loop.

However photosynthesis is very inefficient at harvesting sunlight, absorbing less than 1% of the energy that hits photosynthesizing cells.

Electroactive microbes allow the replacement of biologically based light harvesting with photovoltaics. Such microbes can absorb tiny amounts of electricity in into their metabolism and use this energy to convert CO2 to biofuels. The approach shows considerable potential for producing biofuels at higher efficiencies.

The authors note that non-biological processes for using electricity for carbon fixation (assimilating carbon from CO2 into organic compounds, such as biofuels) is beginning to meet and even exceed microbes' abilities. However, electrochemical technologies so far are not good at producing the complex molecules needed for biofuels and polymers.

Again, engineered electroactive microbes could be used to convert these simple molecules into considerably more complicated ones.

Combinations of engineered microbes and electrochemical systems could drastically surpass the efficiency of photosynthesis. Therefore, a design that couples the two systems could provide a promising solution for energy storage, according to the authors.

"From the calculations that we have done, we think it's definitely possible," Salimijazi said.

The paper features performance data detailing biological and electrochemical designs for carbon fixation.

The current study is "the first time that anybody has gathered in one place all of the data that you need to make an apples-to-apples comparison of the efficiency of all these different modes of carbon fixation," Barstow said.

In the future, the researchers intend to use the data they assembled to test numerous possible combinations of biological and electrochemical and components, and find the best combinations out of the many choices.

Erika Parra, a principal at MultiPHY Laboratories, Inc., is a co-author of the paper.

Support for the study came from Cornell and the Burroughs-Wellcome Fund.