Lignin disruption and ligninolytic enzyme activity in the symbiotic system of the <i>Macrotermes barneyi</i> termite

Fungus-farming termites efficiently degrade recalcitrant lignocellulose through a symbiotic relationship with Termitomyces and the gut microbiome, making them successful key decomposers in (sub)tropical ecosystems. Despite extensive research on plant biomass decomposition, the mechanisms of lignin degradation in fungus-farming termites remain elusive. In view of this information gap, the present study employed several analytical approaches and ligninolytic enzyme assays to investigate lignin modification in the symbiotic system of a fungus-farming termite, Macrotermes barneyi. The results revealed the structural modification of lignin across different points of the degradation process. Enzyme assays of termite guts and fungus combs showed the obvious differences in ligninolytic enzyme activity at different sites of decomposition, likely initiating the modification of lignin. The findings of the current study support the hypothesis that although young workers start the modification of lignin to some extent, they largely leave the lignin monomers p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) intact. Most of the lignin-derived compounds are transferred to the fresh comb, where the majority of lignin modification begins and continues in mature and older parts of the comb. This study provides new insights into biomass degradation within the microsymbiotic system of an insect. A better understanding of these mechanisms has the promising potential for unlocking new lignin-degrading agents for the production of renewable energy.