Cellulosic biofuels could become a commercial reality with new enzyme

Source: By Biofuels International • Posted: Wednesday, September 20, 2017

Three years ago, scientists at the US’ National Renewable Energy Laboratory discovered an enzyme that proves adept at breaking down cellulose fibres regardless of whether their crystalline structure is simple or highly complex. According to the research, no other enzyme has shown this ability.

Now, in a follow-up paper, the researchers have looked at the significant worth the enzyme, CeIA, could have for biofuel production.

The original research showed that CeIA, which comes from Caldicellulosiruptor bescii, could convert biomass to sugars faster than competing catalysts in commercial enzyme preparations. The new study points to how the enzyme could help remove one of the main technical and economic barriers preventing cellulosic biofuels from becoming a commercial reality.

Breaking down the crystalline structure of cellulose fibre in plant cell walls has long proven a problem for cellulases, with fungal enzymes tested to date unable to easily break down fibres with high crystalline content so that the material can be converted into biofuel. CeIA however, is unaffected by the level of crystalline content.

“CelA is able to break down cellulose with high crystallinity the same as low crystallinity, which has never been shown for any other cellulase,” said Yannick Bomble, a senior research scientist at NREL and the senior author of the paper. “The better the cellulase is, the quicker you can convert biomass to simple sugars so the cheaper the process will get.”

Bomble and colleagues’ research looked at how CeIA performed in breaking down and interacting with the components of cell walls in corn stove: glucan, xylan and lignin. Chemical pretreatments were used on corn stover and silky fibres called cotton linters, leaving behind various amounts of the components and varying degrees of crystallinity.

The only obstacle to CeIA was lignin, the component which gives rigidity to cell walls. With some of the chemical pretreatments, some lignin remained, stopping the enzyme.

“If it binds to lignin, it’s just stuck. It can’t process or break down biomass any longer,” Bomble said. “When that happens, you lose the enzyme. The more enzymes you lose to non-productive binding, the less efficient the conversion. That’s usually the problem. This is why we’re working on strategies to prevent CelA’s binding to lignin but retain the vital affinity to cellulose.”