Innovative Discovery Paves the Way for Eco-Friendly Industrial Chemicals from Trees

Lignin, the polymer that provides structure and durability to trees, has posed significant challenges. The NC State team has now pinpointed the particular molecular trait of lignin — its methoxy content — which affects the feasibility of using microbial fermentation to convert trees and other plants into industrial chemicals.

According to Robert Kelly, the lead author of a study published in the journal Science Advances, these discoveries bring us closer to developing industrial chemicals from trees as a viable and environmentally-friendly alternative to petroleum-based chemicals.

Kelly’s team previously demonstrated that certain thermophilic bacteria, which thrive in extreme environments like Yellowstone National Park’s hot springs, can degrade cellulose in trees, but “not to a significant extent,” he elaborated. “In other words, this doesn’t produce enough material economically or environmentally favorable for industrial chemical production.”

As Kelly indicates, “It turns out there’s more at play than just low lignin levels.”

To address the high lignin issue in trees, Kelly has been collaborating for over a decade with Associate Professor Jack Wang, who leads NC State’s Forest Biotechnology Program and is associated with the N.C. Plant Sciences Initiative.

In a 2023 article in the journal Science, Wang and his team employed CRISPR genome editing to produce poplar trees with altered lignin levels and compositions. They selected poplar trees because they are fast-growing, require minimal pesticides, and thrive on less fertile lands where food crops are challenging to cultivate.

Kelly’s team discovered that some of these CRISPR-edited trees were suitable for microbial degradation and fermentation, while others were not. As former Ph.D. student Ryan Bing, now a senior metabolic engineer at Capra Biosciences in Virginia, explained, these bacteria display varying preferences for different types of plant matter.

“We can leverage the ability of certain thermophilic bacteria from locations like Yellowstone to digest plant materials and transform them into useful products. However, these bacteria have diverse preferences for varying plant types,” Bing said.

“Our inquiry focused on what differentiates one plant from another in terms of digestibility,” he added. “We found clarity through examining how these bacteria consume plant materials with different compositions.”

In a subsequent study, Kelly and Bing evaluated how effectively a genetically modified bacterium, originally isolated from Kamchutka, Russia, named Anaerocellum bescii, decomposed Wang’s engineered poplar trees differing in lignin levels and compositions.

The results showed that a lower methoxy content in lignin correlated with greater degradability.

“This resolved the enigma of why simply lower lignin wasn’t the sole factor — the details mattered,” Kelly remarked. “Low methoxy levels likely enhance cellulose accessibility to the bacteria.”

Wang produced low-lignin poplars for improved papermaking and fiber products, yet the latest findings suggest that engineered poplars with both low lignin and low methoxy content are most effective for chemical production via microbial fermentation.

While Wang’s engineered poplars thrive in controlled environments, field tests have yet to yield results. Kelly previously illustrated that low lignin poplar trees can be transformed into industrial chemicals like acetone and hydrogen gas, demonstrating favorable economic outcomes alongside minimal environmental impact.

If these trees perform well in real-world conditions and “if we continue our efforts,” Kelly stated, “we will be able to utilize microbes to generate substantial quantities of chemicals from poplar trees, now that we’ve identified the key factor to watch — the methoxy content.”

This provides researchers like Wang with a distinct target for developing poplar varieties most suited for chemical production. Wang and his team have recently launched field trials of advanced lignin-modified poplar trees to explore this topic further.

Currently, extracting chemicals from trees can be achieved using traditional methods — chopping the wood into smaller segments and applying chemicals and enzymes for pretreatment before further processing.

Employing engineered microbes for lignin breakdown presents several advantages, such as reduced energy consumption and diminished environmental impact, according to Kelly.

Enzymes can convert cellulose into simple sugars; however, they require frequent additions throughout the process. In contrast, certain microorganisms continually produce essential enzymes, making the microbial approach more cost-effective, he noted.

“They not only efficiently break down cellulose but also ferment it into products, such as ethanol — all in one process,” Kelly emphasized. “The high operating temperatures preferred by these bacteria also eliminate the need for sterile conditions, unlike less thermophilic microorganisms, which require strict contamination controls,” he added. “This allows the process of converting trees into chemicals to function like a conventional industrial method, increasing its likelihood of widespread adoption.”

Daniel Sulis, a co-author of the Science Advances publication and a postdoctoral researcher in Wang’s lab, emphasized the pressing need for research that mitigates reliance on fossil fuels, especially in light of environmental disasters linked to climate change.

“A viable solution may lie in utilizing trees to fulfill society’s demands for chemicals, fuels, and other bio-based products while protecting both the planet and human wellbeing,” Sulis stated.

“These discoveries not only advance the field but also set the stage for further innovations in utilizing trees for sustainable bio-based solutions.”