NOVELTY - Preparation (M1) of a microorganism Consortium, involves: providing a biogas-producing microorganism consortium cultured until complete fermentation preferably on animal manure or plant substrate; adding microorganism Consortium and protein monosubstrate to biogas fermentor; culturing microorganism Consortium on protein monosubstrate; adding portions of protein monosubstrate multiple times to fermentation mixture; monitoring fermentation process; determining that Consortium is stable and produces methane-containing biogas; and collecting microorganism.    USE - For fermenting a substrate of high protein content with a concomitant production of methane containing biogas; for increasing biogas production by addition of the microorganism Consortium to a biogas fermentor comprising a substrate of protein content or by addition of a protein containing substrate to a biogas fermentor comprising the microorganism Consortium (claimed); and for production of microorganism Consortium capable of producing methane containing biogas by fermenting a substrate containing at least 75%, preferably at least 90% protein, or more preferably a protein monosubstrate through adaptation to the substrate.    ADVANTAGE - The microorganism Consortium is capable of fermenting a protein monosubstrate, preferably is capable of producing biogas of at least 500 ml/g, preferably at least 600 ml/g, more preferably at least 700 ml/g in relation to organic dry-matter content, and maintaining the production of biogas for at least 1 month or preferably for at least 2 months.    DETAILED DESCRIPTION - Preparation (M1) of a microorganism Consortium, where the Consortium is capable of fermenting, together with a simultaneous production of methane-containing biogas, a substrate having at least 75% protein content, preferably at least 90% protein content or highly preferably a protein monosubstrate, by adaptation to the substrate, involves: providing a biogas-producing microorganism Consortium cultured until complete fermentation preferably on animal manure and/or plant substrate; adding the microorganism Consortium and a protein monosubstrate to a biogas fermentor; culturing the microorganism Consortium on the protein monosubstrate thereby inducing the fermentation of the protein containing substrate; adding further portions of the protein monosubstrate multiple times to the fermentation mixture in the biogas fermentor during culturing time; monitoring the fermentation process in the fermentation mixture; determining that the Consortium is stable and is adapted to the substrate once the consortium is found stable upon monitoring, and preferably determining that the Consortium produces methane-containing biogas, preferably biogas of at least 50% methane-content on the substrate; and collecting the microorganism Consortium which is stable and adapted to the substrate from the fermentation mixture. INDEPENDENT CLAIMS are included for the following: 1) a biogas producing microorganism Consortium comprising proteolytic and/or peptidolytic, acetogenic and methanogenic microorganisms and which is obtained by the method (M1); or is capable of fermenting a substrate having a protein content of at least 75%, preferably at least 90% and an organic dry-matter content of at least 4 g/1, preferably 5 g/1, more preferably at least 6 g/1 relative to the fermentor volume, with a concomitant production of methane-containing biogas, and comprising proteolytic bacteria of the Gammaproteobacteria class, denitrifying bacteria, cellulolytic, peptide degrading and/or amino acid degrading and/or thiosulfate reducing bacteria of the Clostridia class, and preferably the consortium comprises at least 20%, preferably 20-50%, more preferably 22-40% bacteria belonging to the Gammaproteobacteria class, preferably to the Pseudomonadales order, and the Consortium comprises less than 50%, more preferably 10-40%, especially 20-30% bacteria belonging to species of the Clostridia class, preferably of the Clostridiales order and of the Thermoanaerobacterales order; and 2) fermenting (M2) a substrate of high protein content with a production of biogas, involving: providing the biogas fermentor a fermentation mixture comprising a microorganism Consortium and a substrate of at least 70% protein, where the fermentation mixture is fermented; and collecting or utilizing the biogas.