For decades, lignin has been one of researchers’ most persistent hurdles to a bio-based fuel economy. As the organic polymer that binds plant cell, vessel and fiber cell walls, lignin resists chemical and enzymatic processing and thus acts as a structural barrier to converting biomass into liquid fuels.
Curtis Wilkerson, a Michigan State University associate professor and Great Lakes Bioenergy Research Center (GLBRC) scientist, collaborated with John Ralph, a University of Wisconsin–Madison professor of biochemistry and biological systems engineering and the Plants Leader within the GLBRC, and Shawn Mansfield, a professor at the University of British Columbia to introduce “zip-lignin” into poplar trees.
The group’s paper, “Monolignol Ferulate Transferase Introduces Chemically Labile Linkages into the Lignin Backbone,” published in Science in 2014, reports on the introduction of the ferulate monolignol transferase gene (FMT), which produces more easily-broken ester linkages into the lignin backbone, in poplar. When grown in the greenhouse, these poplar trees showed no changes in growth habit, yet the lignin was more easily digested.
Broad commercial use
FuturaGene — a Brazil-based Israeli company using biotechnology to ensure the security and sustainability of fiber, fuel and feed — has licensed Wilkerson and Ralph’s zip-lignin technology to improve pulp production in trees.
Tom Herlache, technology manager and assistant director for commercialization for MSU Technologies, was integral in making the connection with FuturaGene. With a doctoral degree in plant pathology and a law degree focused on intellectual property, his background was a natural fit for working on this licensing agreement.
“Seeing the work of our researchers put into practice on an international level has been very rewarding,” Herlache says. “These trees developed with modified lignin have the potential to provide a substantially better feedstock for use in the Kraft process of converting wood into wood pulp. Researchers expect that the altered lignin will reduce both energy and chemical requirements for pulping, which was of high interest to FuturaGene.”
What began as an innovation to improve paper industry processes and dairy forage digestibility is now opening the door to a much more energy- and cost-efficient way to convert biomass into fuel.
The lignin technology has attracted broad interest from companies in industries from paper and biofuel to agriculture and animal feed.
“Currently, we have a paper pulp and forestry company licensing the technology,” Herlache said. “They’re using it because it makes the lignin easier to extract without affecting the strength of the tree.” Easy lignin extraction lowers the number of chemicals and/or amount of heat needed to pulp the wood.
A crop genetics company also is testing the technology to see if it will make forage crops, such as alfalfa and silage corn, more digestible by livestock, thereby increasing feed efficiency.
Clear biofuel benefits
The idea to engineer biomass for easier degradation first took shape in Ralph’s lab two decades ago when he was working at the U.S. Dairy Forage Research Center. In the mid-1990s, Ralph’s group was looking for ways to reduce energy usage in the paper pulping process by more efficiently removing lignin – the polymer that gives plant cell walls their sturdiness – from trees. The group surmised if they could introduce weak bonds into lignin, it would be much easier for chemical processes to break it down.
This approach had clear benefits for the biofuels industry as well, where difficulty in removing and processing lignin remains a major obstacle to accessing the valuable sugars contained within biomass, adding energy and cost to the production of biofuels.
Seeing an opportunity to carry out Ralph’s concept in poplar, GLBRC researchers pooled their expertise to successfully engineer poplars highly amenable to degradation and, by extension, to industrial processing.
“I guarantee John Ralph and I would never have met without the GLBRC,” Wilkerson says. “When I first met John at a science meeting, I knew very little about lignin. But I ended up sharing some techniques I’d been using for totally different projects that I thought might be useful for his ‘zip-lignin’ research. The collaboration really grew from there.”
Other benefits and applications of this technology:
- Better cellulosic biomass feedstock: Wood, dedicated energy crops, or crop residues containing zip-lignin could serve as better feedstocks for cellulosic biofuels by providing less expensive and more efficient extraction of fermentable sugars, particularly in processes involving ammonia or other alkaline pretreatment. It is expected that the altered lignin will reduce energy and chemical and enzyme requirements for biomass processing.
- Improved lignin polymer extracts: Improved lignin may be extracted as longer polymers, which makes the improved lignin useful as a chemical substrate for carbon fiber production and other uses.
The GLBRC is led by the University of Wisconsin-Madison, with Michigan State University as a major partner, and is one of three bioenergy research centers established in 2007 by the U.S. Department of Energy (DOE). GLBRC performs the basic research that generates technology to convert cellulosic biomass to ethanol and other advanced biofuels.
Wilkerson describes their paper as, “a rare, top-down approach to engineering plants – in this case poplars – for digestibility.” Poplars, a fast-growing crop widely planted throughout the United States and Canada, are particularly valuable to the bioenergy, bio-products, and fiber industries.
“By designing poplars for deconstruction,” Wilkerson says, “we can improve the degradability of a very useful biomass product. Poplars are dense, easy to store, and they flourish on marginal lands not suitable for food crops, making them a non-competing and sustainable source of biofuel.”