UC Davis Scientists Boost Production in Green Cell Factories

By Becky Oskin

Cyanobacteria, one of Earth’s oldest life forms, offer a promising new source of petroleum-free fuels and chemicals. However, economies of scale currently make it challenging for these tiny creatures to compete with fossil fuels. Now, scientists at UC Davis are closer to meeting these challenges with a new advance that improves the production and growth rate of cyanobacteria.

Cyanobacteria culture

UC Davis chemist Shota Atsumi is engineering these cyanobacteria to produce biofuels. (Photo by T.J. Ushing)

Visiting scholar Masahiro Kanno, graduate student Austin Carroll and chemistry professor Shota Atsumi introduced new genetic pathways into cyanobacteria that could help make microbe-based chemical production systems smaller and easier to operate.

“In our daily life, 99 percent of the chemicals come from fossil fuels,” Atsumi said. “Biology has the possibility to replace petroleum and reduce greenhouse gases.”

In a study published March 13, 2017, in the journal Nature Communications, the UC Davis scientists showed cyanobacteria can make significant amounts of 2,3-butanediol (23BD), a raw material for fuels and chemicals, in both light and dark conditions. The best strain produced 13 grams per liter (g/l) of 2,3-butanediol, at a rate of 1 gram per liter per day (g/l/d). “This productivity exceeds any previously reported values for cyanobacterial chemical production,” Atsumi said.

To encourage faster chemical production by cyanobacteria, the researchers searched online databases for enzymes that boost the conversion of carbon dioxide to organic compounds. The team inserted the DNA for these enzymes into cyanobacteria. The new chemical pathway allows cyanobacteria to convert carbon dioxide and glucose into 2,3-butanediol at the 10-gram scale, which could be competitive with conventional sources. In previous work by Atsumi’s lab, researchers rewired cyanobacteria to grow without the need for natural sunlight, which would enable biofuel production 24-hours a day. Cyanobacteria resemble bacteria, but they also have blue-green pigments that allow them to harvest the sun’s energy through photosynthesis.

Related work by the lab team suggests high efficiency production may be possible with LED light sources instead of sunlight, allowing the microbes to grow indoors and reducing contamination risk, Atsumi said.

The work was supported by Japanese chemical manufacturer Asahi Kasei Corp.

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Becky Oskin writes for the Division of Mathematical and Physical Sciences, College of Letters and Science. Follow her on Twitter @beckyoskin.

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