282241 Critical and Adequate Pretreatment of Biomass for Sugar Release by Wood-Feeding Termite
The lack of efficient and cost-effective pretreatment technology is still a limiting factor for lignocellulosic biofuels. The heterogeneous and irregular arrangement of lignin construction results in resistance to saccharification, thus severely hindering biochemical conversion of lignocellulosic biomass to fermentable sugars. Lignin framework also inhibits cellulase function by competitive adsorption, chemical inhibition, and steric hindrance. To remove lignin, existing biomass conversion schemes typically rely on a combination of thermochemical treatments that require energy and input of chemicals. Nature, on the other hand, has developed through evolution efficient biological systems for extracting energy from plant materials to power the lives by effectively deconstructing lignocellulose under natural conditions. With adequate understanding, these biological systems can be harnessed for the production of bioenergy sustainably from renewable lignocellulosic biomass. The high efficiency of cellulose utilization by wood-feeding termite in terms of rate and extent (95% of cellulose in wood within 24 hrs) makes it a promising model to study and mimic. We have been exploring the unique lignin unlocking process in wood-feeding lower termite Coptotermes formosanus (Shiraki). Our results show that termite-induced lignin pretreatment is not achieved by savage degradation, but selectively modification of functional group, cleavage of ether linkage within lignin and ester/ether linkage between lignin-hemicellulose and lignin-cellulose. Such modification results in alleviation of physical and chemical inhibition effect of lignin on cellulases, together with alteration of the three dimensional structure of lignin, which unlocks cellulose fiber from protection. The results also suggested that during the lignin structural modification by termite, a non-enzymatic catalyzing system as the key to the selectivity of lignin modification by termites. The in-vitro mimicking of this non-enzymatic system with umol level concentrations of the chemicals results in alleviation of the lignin inhibition effect on enzymatic cellulose hydrolysis.
Notably, the lignin-modifying system with low chemical concentration was able to selectively act on lignin under neutral pH condition and room temperature. It left lignin backbone alone, producing negligible lignin-derived inhibitors for subsequent cellulose hydrolysis and sugar fermentation. Meanwhile, the residual lignin backbone could be used for other purposes such as value-added lignolytic co-products. This new pretreatment process inspired by termites is from but beyond the nature, which performed lignin pretreatment as efficiently, robust and environmentally-friendly as termites. The information is critical for filling the existing knowledge and technology gaps in sustainable and economical biofuel and value-added chemicals production from lignocellulosic biomass.
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