Investigating the digestive microbiota of detritivores as a bioreactor of leaf litter decomposition in freshwater ecosystems – DIET

The process of plant litter decomposition is central in the global carbon cycling, and this process is substantially supported by freshwater ecosystems. Headwater streams receive massive inputs of autumn-shed riparian leaves which are subsequently decomposed by the interplay of microbial decomposers and detritivorous invertebrates, conditioning and fragmenting the leaves. The decomposition of this litter involves a diverse set of lignocellulose-degrading enzymes, pivotal for the transfer of litter-derived carbon through freshwater ecosystems. The role of leaf-conditioning communities and detritivores in lignocellulose breakdown has been extensively studied, but the influence of the digestive microbiota (DM) of detritivores has never been isolated from that of their host. This project aims at determining the influence of the DM of detritivores on the process of leaf litter decomposition and on the carbon transfer in freshwater ecosystems. The project will be based on the Asellidae model (detritivorous isopods) and combine three complementary approaches: metagenomics, DNA Stable Isotope Probing and biogeochemistry. Axis 1 will develop a metagenomic approach to functionally characterize the DM of 10 Asellidae species and determine whether their DM display unique metabolic capacities of lignocellulose breakdown, which would make their digestive tract an essential bioreactor of this process. Axis 2 will implement a DNA-SIP approach on 4 of these species to experimentally identify the key members of the DM effectively degrading lignocellulose, and determine whether they differ between isopods. Axis 3 will be based on the induction of a digestive dysbiosis (with antibiotics) in 4 of these species to quantify the effect on litter decomposition rate, C assimilation in isopod tissues, DOC and CO2 production. This axis will allow to measure the influence of the DM on the efficiency of litter decomposition, and on the transfer of litter-derived carbon.