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Front. Microbiol. | doi: 10.3389/fmicb.2018.02222

Screening of phytophagous and xylophagous insects guts microbiota abilities to degrade lignocellulose in bioreactor

Amandine Gales1,  Lucile Chatellard1, Maider Abadie2, Anais Bonnafous1,  Lucas Auer2,  Helene Carrere1,  Jean Jacques Godon1, Guillermina Hernandez-Raquet2 and  Claire Dumas1, 2*
  • 1Laboratoire de Biotechnologie de l'Environnement (INRA), France
  • 2UMR5504 Laboratoire d'Ingénierie des Systèmes Biologiques et des Procédés (LISBP), France

Microbial consortia producing specific enzymatic cocktails are present in the gut of phytophagous and xylophagous insects; they are known to be the most efficient ecosystems to degrade lignocellulose. Here, the ability of these consortia to degrade ex-vivo lignocellulosic biomass in anaerobic bioreactors was characterized in term of bioprocess performances, enzymatic activities and bacterial community structure. In a preliminary screening, guts of Ergates faber (beetle), Potosia cuprea (chafer), Gromphadorrhina portentosa (cockroach), Locusta migratoria (locust), and Gryllus bimaculatus (cricket) were inoculated in anaerobic batch reactors, in presence of grounded wheat straw at neutral pH. A short duration fermentation of less than 8 days was observed and was related to a drop of pH from 7 to below 4.5, leading to an interruption of gas and metabolites production. Consistently, a maximum of 180mgeq.COD of metabolites accumulated in the medium, which was related to a low degradation of the lignocellulosic biomass, with a maximum of 5 and 2.2% observed for chafer and locust gut consortia. The initial cell-bound and extracellular enzyme activities, i.e. xylanase and β-endoglucanase, were similar to values observed in the literature. Wheat straw fermentation in bioreactors leads to an increase of cell-bounded enzyme activities, with an increase of 145% for cockroach xylanase activity. Bacterial community structures were insect dependent and mainly composed of Clostridia, Bacteroidia and Gammaproteobacteria. Improvement of lignocellulose biodegradation was realized in successive batch mode at pH 8 using the most interesting consortia, i.e. locust, cockroaches and chafer gut consortia. In these conditions, lignocellulose degradation increased significantly: 8.4, 10.5 and 21.0% of the initial COD was degraded for chafer, cockroaches and locusts, respectively in 15 days. Consistently, xylanase activity tripled for the three consortia, attesting the improvement of the process. Bacteroidia was the major bacterial class represented in the bacterial community for all consortia, followed by Clostridia and Gammaproteobacteria classes. This work demonstrates the possibility to maintain apart of insect gut biological activity ex-vivo and shows that lignocellulose biodegradation can be improved by using a biomimetic approach. These results bring new insights for the optimisation of lignocellulose degradation in bioreactors.

Keywords: Fermentation, biomimetism, insect guts, volatile fatty acids, Microbial Diversity

Received: 20 Apr 2018; Accepted: 31 Aug 2018.

Edited by:

Phil B. Pope, Norwegian University of Life Sciences, Norway

Reviewed by:

Subramanian Sabtharishi, Indian Agricultural Research Institute (ICAR), India
Li Sun, Swedish University of Agricultural Sciences, Sweden  

Copyright: © 2018 Gales, Chatellard, Abadie, Bonnafous, Auer, Carrere, Godon, Hernandez-Raquet and Dumas. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mrs. Claire Dumas, UMR5504 Laboratoire d'Ingénierie des Systèmes Biologiques et des Procédés (LISBP), Toulouse, France, claire.dumas@insa-toulouse.fr