Engineering bacteria in the quest for green biomanufacturing solutions

• The chemical industry ranks as the largest industrial consumer of gas and oil, prompting the need for greener alternatives.
• Researchers have engineered bacteria to produce carbon-based substances not found naturally, offering exciting possibilities for sustainable biochemical production.
• The scalable approach succeeds in replacing expensive chemicals with naturally derived substances, eliminating toxic solvents and gases.

Did you know the chemical industry holds the title of the largest industrial consumer of gas and oil? In fact, it's the third-largest contributor to direct CO₂ emissions, following closely behind the steel and iron, and cement industries. While it plays a vital role in our modern world, it comes at a significant cost. 

But what if we could find a way to produce essential chemicals without fossil fuels? Well, a recent study has brought us one step closer to that possibility.

Researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC), Berkeley, have joined forces to explore the remarkable capabilities of tiny microbes. They have successfully engineered carbon-based substances that have never previously existed in nature, opening up exciting possibilities for developing sustainable biochemicals.

Interesting Engineering (IE) connected with one of the scientists behind the work—Professor Jay D. Keasling from the Department of Chemical & Biomolecular Engineering at UC Berkeley—to better understand what this novel venture involves. 

'Sweet tooth' engineered bacteria unlock biosynthesis 

"My lab engineers microbes to produce chemicals (fuels, commodity, and specialty chemicals, pharmaceuticals), so this is nature for us," said Keasling. In case you didn't know, this field of science is known as biosynthesis. 

He explained that the microbes in his lab use sugars to make chemicals. These sugars come from plants, which absorb CO₂ from the atmosphere. 

"If the chemicals they produce are burned as fuels, then they will be carbon neutral," he told IE. "If the chemicals end up in materials that are not burned, then those materials are carbon negative, actually removing CO₂ from the atmosphere." 

In the new study, his team combined bacteria's natural processes with a well-known biosynthesis process called the "carbene transfer reaction." The engineered bacteria could produce carbon-based substances not found naturally—called 'new-to-nature products'—while utilizing sugars as their energy source.

Scientists have long wanted to harness carbene transfer reactions in manufacturing fuels, chemicals, and drug discovery. However, these processes were previously limited to small-scale experiments in test tubes, as they required expensive chemicals to drive the reactions. A paper based on the new study describes these chemicals as 'carbene donors and unnatural cofactors.'  

The slower progress of biosynthesis compared to synthetic chemistry can also be attributed to the limitation of enzymatic reactions in living organisms, which restricts the availability of diverse producible compounds.

As a solution, in the new study, the research team replaced expensive chemicals with naturally derived substances that can be produced by genetically engineered bacteria. In doing so, the approach eliminated the need for toxic solvents and gases typically used in chemical synthesis.

"What we showed in this paper is that we can synthesize everything in this reaction—from natural enzymes to carbenes —inside the bacterial cell. All you need to add is sugar, and the cells do the rest,” stated Keasling in a press release.

The paper's first author, Jing Huang, emphasized that this biological process is significantly more environmentally friendly compared to current methods of chemical synthesis.

What is the use of genetically engineered bacteria?

Through their experiments, the researchers observed the bacteria metabolizing sugars and converting them into carbene precursors and other molecules. Notably, a carbene precursor called α-diazoester azaserine, produced by expressing a biosynthetic gene cluster in Streptomyces albus, acted as a carbene donor. 

Additionally, the bacteria developed an 'evolved P450 enzyme' that used those azaserines to create cyclopropanes. Cyclopropanes are high-energy molecules that may one day be utilized in the sustainable synthesis of novel bioactive compounds and advanced biofuels.

"We can now perform these interesting reactions inside the bacterial cell. The cells produce all of the reagents and the cofactors, which means that you can scale this reaction to very large scales" for mass manufacturing, Keasling said in a press release earlier this month.

Talking of scalability, IE was keen for Keasling to elaborate on this. Furthermore, we wanted to learn whether this approach could extend beyond the chemical industry and be implemented in other sectors and of any limitations to consider. 

"That is the million (or multi-billion) dollar question," Keasling told IE. "Scaling any technology can be much more challenging than developing it initially. Our job is to propose the technology and work with companies to implement it."

"Fuels are the most challenging because they are the least expensive things." 

Keasling emphasized that in nearly all instances over the past 30 years, similar technologies have eventually proven scalable, although not always cost-effective. "These technologies can be applied across industries: pharmaceuticals, specialty chemicals, commodity chemicals, fuels," he said.

"Fuels are the most challenging because they are the least expensive things. Commodity chemicals are the next most challenging."

Keasling added that specialty chemicals and pharmaceuticals are less challenging because they can be sold for high costs, which makes economic scaling easier.

When asked about any unforeseen challenges or setbacks encountered during the development and implementation of this technique, Keasling's response was straightforward:

"We always run into challenges and setbacks. We are persistent and don't take "no" readily. If one of our proposed processes doesn't work, then we try another and another until we get something to work," he said.

Exploring the path to sustainable biomanufacturing solutions

Huang highlighted that for every new advance, someone needs to take the first step. "In science, it can take years before you succeed. But you have to keep trying—we can't afford to give up. I hope our work will inspire others to continue searching for greener, sustainable biomanufacturing solutions." he stated in the press release. 

Although the team's carbene donor molecules and alkene substrates for sustainable biomanufacturing are not yet suitable for commercial use, the researchers' remarks underscore the importance of collaboration and ongoing progress in scientific endeavors. 

Their work serves as an inspiration not only to the scientific community but also to a broader audience, encouraging everyone to continuously push boundaries and seek environmentally friendly alternatives. 

"We are always looking to test our technologies in real-world settings. Sometimes our technologies are 20 years ahead of when they will be used at scale. That's okay. What we have created could find application in so many industries. We just don't know which ones yet," concluded Keasling.