Miscanthus sp. biomass could satisfy future biorefinery value chains. However, its use is largely untapped due to high recalcitrance. The termite and its gut microbiome are considered the most efficient lignocellulose degrading system in nature. Here, we investigate at holobiont level the dynamic adaptation of Cortaritermes sp. to imposed Miscanthus diet, with a long-term objective of overcoming lignocellulose recalcitrance. We use an integrative omics approach combined with enzymatic characterisation of carbohydrate active enzymes from termite gut Fibrobacteres and Spirochaetae. Modified gene expression profiles of gut bacteria suggest a shift towards utilisation of cellulose and arabinoxylan, two main components of Miscanthus lignocellulose. Low identity of reconstructed microbial genomes to closely related species supports the hypothesis of a strong phylogenetic relationship between host and its gut microbiome. This study provides a framework for better understanding the complex lignocellulose degradation by the higher termite gut system and paves a road towards its future bioprospecting.

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26Miscanthus sp. is regarded as suitable biomass for different biorefinery value chains. However, due 27 to high recalcitrance, its wide use is yet untapped. Termite is the most efficient lignocellulose 28 degrading insect, and its success results from synergistic cooperation with its gut microbiome. 29Here, we investigated at holobiont level the dynamic adaptation of a higher termite Cortaritermes 30 sp. to imposed Miscanthus diet, with a long-term objective of overcoming lignocellulose 31 recalcitrance. We used an integrative omics approach, comprising amplicon sequencing, 32 metagenomics and metatranscriptomics that we combined with enzymatic characterisation of 33 carbohydrate active enzymes from termite gut Fibrobacteres and Spirochaetae. Adaptation to the 34 new diet was evidenced by reduced gut bacterial diversity and modified gene expression profiles, 35 further suggesting a shift towards utilisation of cellulose and arabinoxylan, two main components of 36Miscanthus lignocellulose. Low identity of reconstructed microbial genomes to microbes from 37 closely related termite species, supported the hypothesis of a strong phylogenetic relationship 38 between host and its gut microbiome. Application-wise, this makes each termite gut system an 39 endless source of enzymes that are potentially industrially relevant. 40This study provides a framework for better understanding the complex lignocellulose degradation by 41 the higher termite gut system and paves a road towards its future bioprospecting. 42 43

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