Updated project metadata. In this study, a complex microbial community from a semi-continues reactor, which only substrate is wheat straw, was incubated in a batch experiment with 13C-cellulose. protein stable isotope probing (protein-SIP) was used to identify the organisms, at high taxonomic resolution, involved in the degradation of cellulose by tracking the incorporation of 13C in the newly synthetized proteins. Thereby providing information regarding identity and function simultaneously and enable the optimization of biotechnologies for biofuels production.