bag containing a forage with a high cellulose content (for example, Panicum virgatum). An orifice is surgically done to the spine making rumen available from the outside through a tampon which avoids the closing of the fistula. The nylon bag is incubated in the rumen 72 hours. After incubation it is important to separate the microorganisms adhered to the vegetable fibres from the ones that are in suspension in the ruminal fluid. Analysis of microbial community specificity To analyze the specificity of the community on the sample, one can compare the diversity of sequences of small subunit ribosomal RNA of the sample with a sample of reference. After extraction and purification of the DNA of the sample, the PCR emulsion technique is used to amplify the genes of the small ribosomal subunit. Then each amplicon is sequenced with the pyrosequencing technique. Once we have the sequences they have to be compared and grouped according to the degree of similarity, to define OTUS (Operational Taxonomic Units)-which are groups of sequences that belong to organisms phylogenetically close. Comparing OTUS of the two samples the differences of both microbial communities could be assessed. Metagenomic sequencing In order to obtain the sequences of lignocelulitic genes an accurate metagenomic analysis is done. Sequencing and assembly of the whole DNA of the sample gives the metagenome of the sample. Identification of carbohydrate active genes The identification of genes that encode for proteins which have fibrolytic activity is done in two steps. First, a bioinformatic analysis is performed. The sequences obtained in the metagenomic analysis are compared with the gene sequences of known fibrolytic proteins (for example the sequences that are on the data base Carbohidrate Active Enzymes (CAZy)). In this first step the number of candidate genes is reduced considerably and these are the ones that are used on the following step. In the second step, a library for protein expression is built. Expression vectors are introduced in E.coli and after the growth of these bacteria the supernatant is tested for biochemical activity on different substrates. Identification of fibrolytic microorganisms To identify to which microorganisms belong the enzymes which have been identified, and check if metagenome assembly was right, a separation of different species of bacteria from the sample can be done by flow cytometry. The use of specific antibodies labelled with fluorochromes makes possible to separate the different cell types of the sample which belong