‘Swiss Army knife’ helps turn algae into biofuel

Scientists have built a protein that streamlines the process of making biofuel from algae. "The multifunctional protein we've built can be compared to a Swiss Army knife," says Raul Gonzalez-Esquer. "From known, existing parts, we've built a new protein that does several essential functions." (Credit: Christian Kitazume/Flickr)

Scientists have figured out a way to streamline the molecular machinery that turns cyanobacteria—also known as blue-green algae—into biofuels.

They fabricated a synthetic protein that not only improves the assembly of the carbon-fixing factory of cyanobacteria, but also provides a proof of concept for a device that might improve plant photosynthesis.

“The multifunctional protein we’ve built can be compared to a Swiss Army knife,” says Raul Gonzalez-Esquer, a doctoral researcher at Michigan State University. “From known, existing parts, we’ve built a new protein that does several essential functions.”

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Gonzalez-Esquer worked with Cheryl Kerfeld, professor of structural bioengineering, who studies bacterial microcompartments (BMCs), to build the protein. BMCs are self-assembling cellular organs that perform myriad metabolic functions, and, in a sense, are molecular factories with many different pieces of machinery.

The scientists modernized the “factory” by updating the carboxysome, a particularly complex BMC that requires a series of interactions involving at least six gene products. The result is a metabolic core that takes CO2 out of the atmosphere and converts it into sugar. To streamline the process, the scientists created a hybrid protein in cyanobacteria, organisms that have many potential uses for making green chemicals or biofuels.

The new protein, described in the current issue of Plant Cell, replaces four gene products, yet still supports photosynthesis. Reducing the number of genes needed to build carboxysomes should facilitate the transfer of carboxysomes into plants. The installation should help plants’ ability to fix carbon dioxide. Improving their capacity to remove CO2 from the atmosphere makes it a win-win, Gonzalez-Esquer says.

“It’s comparable to making coffee. Rather than getting an oven to roast the coffee beans, a grinder to process them, and a brewing machine, we’ve built a single coffeemaker where it all happens in one place. The new tool takes raw material and produces the finished product with a smaller investment.”

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This proof of concept also shows that BMCs can be broken down to the sum of their parts, ones that can be exchanged. Since they are responsible for many diverse metabolic functions, BMCs have enormous potential for bioengineering, Kerfeld says.

“We’ve showed that we can greatly simplify the construction of these factories. We can now potentially redesign other naturally occurring factories or dream up new ones for metabolic processes we’d like to install in bacteria.”

This altered cyanobacterial species won’t be taking over any ponds—or the world—anytime soon. While the improved organisms excel at photosynthesis in a lab setting, they’re ill-prepared to compete with other bacteria. Because they were stripped of four genes, they’re not as flexible as their natural cousins.

“Cyanobacteria have adapted to live in ponds that are drenched by sun, blanketed by shade, frozen solid in the winter, not to mention the other organisms with which they have to compete to survive,” Kerfeld says. “We’ve restricted ours and their ability to grow; they no longer have all of the tools to compete, much less dominate, in the natural environment.”

Source: Michigan State University