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.

Increased hydrolysis of easily digestible biomass may lead to acidosis of anaerobic reactors and decreased methane production. Previously, it was shown that the structure of microbial communities changed during acidosis; however, once the conditions are back to optimal, biogas (initially CO2) production quickly restarts. This suggests the retention of the community functional redundancy during the process failure. In this study, with the use of metagenomics and downstream bioinformatics analyses, we characterize the carbohydrate hydrolytic potential of the microbial community, with a special focus on acidosis. To that purpose, carbohydrate-active enzymes were identified, and to further link the community hydrolytic potential with key microbes, bacterial genomes were reconstructed. In addition, we characterized biochemically the specificity and activity of selected enzymes, thus verifying the accuracy of the in silico predictions. The results confirm the retention of the community hydrolytic potential during acidosis and indicate Bacteroidetes to be largely involved in biomass degradation. Bacteroidetes showed higher diversity and genomic content of carbohydrate hydrolytic enzymes that might favor the dominance of this phylum over other bacteria in some anaerobic reactors. The combination of bioinformatic analyses and activity tests enabled us to propose a model of acetylated glucomannan degradation by Bacteroidetes. IMPORTANCE The enzymatic hydrolysis of lignocellulosic biomass is mainly driven by the action of carbohydrate-active enzymes. By characterizing the gene profiles at the different stages of the anaerobic digestion experiment, we showed that the microbiome retains its hydrolytic functional redundancy even during severe acidosis, despite significant changes in taxonomic composition. By analyzing reconstructed bacterial genomes, we demonstrate that Bacteroidetes hydrolytic gene diversity likely favors the abundance of this phylum in some anaerobic digestion systems. Further, we observe genetic redundancy within the Bacteroidetes group, which accounts for the preserved hydrolytic potential during acidosis. This work also uncovers new polysaccharide utilization loci involved in the deconstruction of various biomasses and proposes the model of acetylated glucomannan degradation by Bacteroidetes. Acetylated glucomannan-enriched biomass is a common substrate for many industries, including pulp and paper production. Using naturally evolved cocktails of enzymes for biomass pretreatment could be an interesting alternative to the commonly used chemical pretreatments.

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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

Background Aerobic granular sludge (AGS) has emerged as a novel wastewater treatment technology and as a suppressing alternative to conventional activated sludge. The development of mathematical models of the AGS process, which can be used for wastewater treatment plant (WWTP) design and optimization, is therefore necessary to support successful implementation of AGS technology. This study aims to develop a zero‐dimensional (0D) AGS model that can be used in engineering practice for the above‐mentioned purposes. Results A laboratory AGS sequencing batch reactor (SBR), removing soluble organic substrate, nitrogen and phosphorus, was fed with artificial wastewater and modelled using a 0D approach. Model development was supported by bacterial characterization using 16S rRNA gene amplicon high‐throughput sequencing. The mathematical model was based on the activated sludge model no. 2d (ASM2d) and extended with both two‐step nitrification as implemented in the wastewater treatment plant simulator Sumo19 (Dynamita SARL) and ammonia nitrogen adsorption and desorption according to the Langmuir model. The variations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, orthophosphate phosphorus and dissolved oxygen concentrations during one cycle of the SBR were successfully reproduced by the model (all Pearson's r values ≥0.93 and all r2 ≥ 0.86). Conclusions The 0D modelling approach was proven to be applicable to AGS. It is possible that the 0D approach can fill the gap that has developed between engineering and research in the biofilm modelling community. The 0D modelling approach therefore merits further exploration using reactors fed with real wastewater, as well as on pilot and full‐scale WWTPs. © 2022 Society of Chemical Industry (SCI).

Background: Termites are among the most successful insects on Earth and can feed on a broad range of organic matter at various stages of decomposition. The termite gut system is often referred to as a micro-reactor and is a complex structure consisting of several components. It includes the host, its gut microbiome and fungal gardens, in the case of fungi-growing higher termites. The digestive track of soil-feeding higher termites is characterised by radial and axial gradients of physicochemical parameters (e.g. pH, O2 and H2 partial pressure), and also differs in the density and structure of residing microbial communities. Although soil-feeding termites account for 60 % of the known termite species, their biomass degradation strategies are far less well known compared to their wood-feeding counterparts. Results: In this work, we applied an integrative multi-omics approach for the first time at the holobiont level to study the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis. We relied on 16S rRNA gene community profiling, metagenomics and (meta)transcriptomics to uncover the distribution of functional roles, in particular those related to carbohydrate hydrolysis, across different gut compartments and among the members of the bacterial community and the host itself. We showed that the Labiotermes gut was dominated by members of the Firmicutes phylum, whose abundance gradually decreased towards the posterior segments of the hindgut, in favour of Bacteroidetes, Proteobacteria and Verrucomicrobia. Contrary to expectations, we observed that L. labralis gut microbes expressed a high diversity of carbohydrate active enzymes involved in cellulose and hemicelluloses degradation, making the soil-feeding termite gut a unique reservoir of lignocellulolytic enzymes with considerable biotechnological potential. We also evidenced that the host cellulases have different phylogenetic origins and structures, which is possibly translated into their different specificities towards cellulose. From an ecological perspective, the capacity to feed on distinct polymorphs of cellulose retained in soil may have enabled this termite species to widely colonise the different habitats of the Amazon basin. Conclusions: Our study provides interesting insights into the distribution of the hydrolytic potential of the highly compartmentalised higher termite gut. The large number of expressed enzymes targeting the different lignocellulose components make the Labiotermes worker gut a relevant lignocellulose-valorising model to mimic by biomass conversion industries.

Background Termites are among the most successful insects on Earth and can feed on a broad range of organic matter at various stages of decomposition. The termite gut system is often referred to as a micro-reactor and is a complex structure consisting of several components. It includes the host, its gut microbiome and fungal gardens, in the case of fungi-growing higher termites. The digestive tract of soil-feeding higher termites is characterised by radial and axial gradients of physicochemical parameters (e.g. pH, O2 and H2 partial pressure), and also differs in the density and structure of residing microbial communities. Although soil-feeding termites account for 60% of the known termite species, their biomass degradation strategies are far less known compared to their wood-feeding counterparts. Results In this work, we applied an integrative multi-omics approach for the first time at the holobiont level to study the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis. We relied on 16S rRNA gene community profiling, metagenomics and (meta)transcriptomics to uncover the distribution of functional roles, in particular those related to carbohydrate hydrolysis, across different gut compartments and among the members of the bacterial community and the host itself. We showed that the Labiotermes gut was dominated by members of the Firmicutes phylum, whose abundance gradually decreased towards the posterior segments of the hindgut, in favour of Bacteroidetes, Proteobacteria and Verrucomicrobia. Contrary to expectations, we observed that L. labralis gut microbes expressed a high diversity of carbohydrate active enzymes involved in cellulose and hemicelluloses degradation, making the soil-feeding termite gut a unique reservoir of lignocellulolytic enzymes with considerable biotechnological potential. We also evidenced that the host cellulases have different phylogenetic origins and structures, which is possibly translated into their different specificities towards cellulose. From an ecological perspective, we could speculate that the capacity to feed on distinct polymorphs of cellulose retained in soil might have enabled this termite species to widely colonise the different habitats of the Amazon basin. Conclusions Our study provides interesting insights into the distribution of the hydrolytic potential of the highly compartmentalised higher termite gut. The large number of expressed enzymes targeting the different lignocellulose components make the Labiotermes worker gut a relevant lignocellulose-valorising model to mimic by biomass conversion industries.