Discovery of lignin’s molecular properties could help turn trees into affordable, greener industrial chemicals

Trees are the most abundant natural resource on Earth’s landmass, and North Carolina State University scientists and engineers are using trees as a sustainable and environmentally friendly alternative to producing industrial chemicals from petroleum. We are currently discovering ways to utilize it.

Lignin is a polymer that makes trees hard and resistant to deterioration, but it has proven problematic. Researchers at North Carolina State University know why. They identified a specific molecular property of lignin, namely its methoxy content. This determines how difficult or easy it is to turn trees and other plants into industrial chemicals using microbial fermentation.

The discovery brings us one step closer to producing industrial chemicals from trees as an economical and environmentally sustainable alternative to petroleum-based chemicals, according to the journal Science Advances, which details the discovery. said Robert Kelly, corresponding author of the paper.

Kelley’s group had previously shown that certain extremely thermophilic bacteria, such as those that thrive in hot springs in Yellowstone National Park, can break down cellulose in trees, but “not to a large extent,” he said. said. “In other words, it is not at a level that makes economic and environmental sense for producing industrial chemicals.”

“It turns out that the decline in lignin is not the only culprit,” Kelly explained.

To get around the high lignin problem in trees, Kelly, director of North Carolina’s biotechnology program and Alcoa professor in the Department of Chemical and Biomolecular Engineering, collaborated with Associate Professor Jack Wang, director of the forest biotechnology department, to I have been conducting research for over a year. program at North Carolina State College of Natural Resources. Wang is also a faculty member of the NC Plant Sciences Initiative.

As reported in the journal Science in 2023, Wang and colleagues used CRISPR genome editing technology to create poplar trees with altered lignin content and composition. They focused on the poplar trees. That’s because poplar trees grow quickly, require minimal use of pesticides, and grow in remote areas where it’s difficult to grow food crops.

Kelly’s group found that some, but not all, of these CRISPR-edited trees work well for microbial degradation and fermentation. As his former PhD student Ryan Bing explained, these bacteria were found to have different appetites depending on the type of plant.

“We can take advantage of the ability of certain thermophilic bacteria found in hot springs in places like Yellowstone National Park to feed on plant material and convert it into desired products. However, these bacteria Different types have different appetites,” Bing said. He currently works as a senior metabolic engineer at Capra Biosciences in Sterling, Virginia.

“The question was why. What makes one plant better than another?” he explained. “We found the answer to this by observing how these bacteria feed on plants of varying composition.”

In a follow-up study, Kelly and Bing investigated how well a genetically engineered bacterium, Anaerocellum bescii, originally isolated from hot springs in Kamchutka, Russia, degraded Wang’s engineered poplar wood, which has a significantly different lignin content and composition. Tested.

The researchers found that the lower the wood’s lignin methoxy content, the easier it is to break down.

“This solves the mystery of why low-grade lignins aren’t the only key. The devil was in the details,” Kelly said. “Lower methoxy content may make cellulose more available to bacteria.”

Wang had been developing low-lignin poplar suitable for papermaking and other textile products, but recent research has shown that engineered poplar, which has not only low lignin but also low methoxy content, could be used to make chemicals through microbial fermentation. It is suggested that it is optimal.

Wang’s artificial poplars grow well in greenhouses, but field test results are not yet available. Kelly’s group has previously shown that low-lignin poplar wood can be converted into industrial chemicals such as acetone and hydrogen gas, with less environmental impact and favorable economic outcomes.

If these trees hold up in the field and “we continue to work toward our goal,” Kelly says, “poplar trees will produce microorganisms that will produce a ton of chemicals. Now, methoxy-containing We know the metric to look for: volume.” ”

This gave researchers like Wang a concrete target for producing poplar strains ideal for chemical production. Wang and colleagues recently began field trials of highly lignin-modified poplar trees to address this issue.

At present, producing chemicals from wood can be carried out in the traditional way by chopping the wood into small pieces and pre-treating it with chemicals and enzymes for further processing.

Kelly said there are benefits to using engineered microorganisms to break down lignin, including lower energy requirements and reduced environmental impact.

Enzymes can be used to break down cellulose into simple sugars, but the enzymes must be continually added to the process. Meanwhile, certain microorganisms continually produce important enzymes that make microbial processes more economical, he said.

“They can also work much better than enzymes or chemicals,” Kelly added. “It not only breaks down the cellulose, but also ferments the cellulose to produce products such as ethanol, all in one step.

“Because these bacteria grow at high temperatures, there is also no need to work under sterile conditions, which would require using less thermophilic microorganisms to avoid contamination,” he added. “This means that the process of turning trees into chemicals can be operated like traditional industrial processes, making it more likely to be adopted.”

Daniel Soulis, another author of the paper and a postdoctoral fellow in Wang’s lab, said the environmental disaster caused by climate change makes it urgent for research to find ways to reduce dependence on fossil fuels. He said it highlights the need.

“One promising solution is to harness trees to meet society’s needs for chemicals, fuels and other bio-based products, while protecting the planet and human well-being,” Sulis added. .

“These discoveries not only advance the field but also lay the foundation for further innovations in using trees for sustainable bio-based applications.”