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Friday, September 17, 2021

The power of the sun

As nations grow and the supply of fossil fuels diminishes, demands for alternative fuel sources rise. The miniscule blue-green algae, or cyanobacteria, provide a means of producing alternative fuels and other commercial products.

In UC Davis, Shota Atsumi, assistant professor of chemistry, and his research group have developed a method to enable cyanobacteria to produce 2,3-butanediol, a type of butane. This butane is a key chemical in producing fuels and solvents.

As a result of the single-celled nature of cyanobacteria, it is easier to introduce DNA fragments that help with the synthesis of 2,3-butanediol from pyruvate, a sugar found in plants.

“Cyanobacteria [are] easy to manipulate. [They] can grow much faster than plants, and the carbon dioxide exchange is faster,” Atsumi said. “In the cynanobacteria, they don’t have any enzymes to create [butane], but [they] can produce pyruvate. We can create a DNA fragment that produces a gene encoder enzyme, and then we install the fragment into a chromosome on the cyanobacteria.”

In essence, the cyanobacteria become genetically modified to create 2,3-butanediol from pyruvate.

In addition, the cyanobacteria have relatively easier and cheaper means of cultivation. While yeast and E. coli have been considered for biofuel production, they require sugar to start their cultures — cyanobacteria does not.

“We use a shake flask and put [the cyanobacteria culture] at 30 degrees Celsius. The cyanobacteria can use light energy and carbon dioxide to grow,” Atsumi said.

Brendan Higgins, a graduate student researcher in UC Davis’s Jean VanderGheynst’s lab, gave a few more reasons why algae are considered.

“The algae we work with [are] microalgae and it produces a lot of oil, like vegetable oil — high-energy molecules,” he said.

Jean VanderGheynst, a professor of UC Davis’s department of biological and agricultural engineering and head of the VanderGheynst Lab that works with different microorganisms such as chlorella, also gave these reasons for why algae in general are good organisms to work with.

“Algae are very attractive because they can be grown in a way where they have a very high photosynthetic efficiency. Algae are also very interesting in a biofuel perspective because they can be grown on marginal lands using waste waters.”

This makes it possible for algae to be a good biofuel organism because they do not directly compete with other food crops such as corn.

“In many cases [the cyanobacteria] can treat the water as they accumulate oil and starch that can be converted into biofuel. Algae are often able to remove some of the components in the water that makes it difficult to irrigate land,” VanderGheynst said.

According to VanderGheynst, algae are a superior producer of biofuels because other crops used for biofuel production, such as corn, have evolved to resist being broken down by microorganisms.

While algae are superior to crops such as corn for making biofuels, mass cultivation of the 2,3-butanediol-producing-cyanobacteria in open ponds poses several problems.

“Using open ponds is easy but has many issues such as slow growth and contamination,” Atsumi said.

Since cultivation in ponds depends on natural weather and day-night cycles, the algae are at a higher risk for contamination from other organisms, and growth stops completely during the night hours.

“The main concern for us as algae researchers is contamination of our cultures,” Higgins said. “You could spend millions of dollars creating an organism that creates valuable product. It’ll suffer some contamination or shutdown period. You could restart with a fresh culture, but if you invest millions of dollars in that organism you probably want to make sure it can not be contaminated.”

With these factors in mind, Atsumi intends to step up the small-lab cultivation of 2,3-butanediol cyanobacteria to a large scale through closed structures called photobioreactors. However, there are still challenges to the photobioreactor system.

“Design of photobioreactors that maximize solar energy capture and conversion to biofuels has been one of the major challenges in this field,” Atsumi said.

Higgins added, “They can cost a lot at setup. Usually photobioreactors are for products like pharmaceuticals or other more valuable products.”

Even if the value of large-scale cultivation of 2,3-butanediol producing cyanobacteria does not seem cost efficient, Atsumi’s work has contributed much to the other fields regarding biofuels. His techniques for inserting DNA fragments into single-celled organisms could further research regarding genetic modification of single-celled organisms.

“We need chemists, biologists [and] engineers all working on this problem of producing biofuels from algae economically,” VanderGheynst said. “The collaboration is critical for what an engineer would do in her lab.”

VICTORIA TRANG can be reached at science@theaggie.org.

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