Termite Gut Microbiota Contribution to Wheat Straw Delignification in Anaerobic Bioreactors

Lignin is a major lock for lignocellulose valorizationin biorefineries, prompting a need tofind newligninolytic systems. Termites are efficient lignocellulose degraders, and a large part ofthis ability comes from its anaerobic gut microbiome. However, thepotential of termite gut microbiomes to degrade lignin underanaerobicconditions has yet to be elucidated. By applying wetchemistry, multidimensional NMR spectroscopy, and quantitative13C-IS py-GC-MS, we determined the chemical and structuralcharacteristics of wheat straw digested by the gut microbiomes ofhigher termitesNasutitermes ephratae,Nasutitermes lujae,Micro- cerotermes parvus, andTermes hospesimplemented in anaerobicbioreactors. Interestingly, all gut microbiomes managed to removelignin (up to 37%), although hemicellulose (mean 51%) andcellulose(mean 41%) were degraded more efficiently. Important structural differences, indicative of ligninolytic action, were discerned in the residual lignin. For the studied termite gut microbiomes, a slight decrease of S/G ratio was observed upon digestion, whereas lignin’s interunit linkages and Cα-oxidized moieties, including benzaldehyde and hydroxypropiovanillone/syringone substructures, accumulated. Additionally, tricin terminal units were clearly depleted, along with decreases inp-coumarate and ferulate pendant units. At least 80% of the observed delignification is estimated to be due to the removal of“true”lignin, with the remainder being explained by the removal of hydroxycinnamic acids and tricin. Collectively, ourfindings suggest a partial deconstruction of lignin, with“peripheral”lignin subunits being preferentially targeted. The present work thus provides new insights into the anaerobic deconstruction of lignin by termite gut microbiomes.