The replacement of fossil fuels by renewable energies is probably one of the biggest challenges of the 21st century. Among the different energies, hydrogen is one of the most promising. The new concepts for the production of "renewable H2" are extremely promising (but still far from economic viability) and require fundamental research to understand and then optimize these processes. Produce and use renewable H2 can lead to innovative processes responding to societal, environmental and scientific interests. To date most of the works on the H2 production, via a biological pathway, focus on pure or genetically modified cultures, and the use of simple substrates. More recently, the use of microbial mixed cultures has emerged with regard to their robustness, the wide panel of usable substrates, their metabolic adaptability and flexibility. A new idea is that, more than their intrinsic properties, there are the interactions between microorganisms that confer a specific behaviour and resistance properties to a bacterial community. To date, very few studies integrate the role and the control of these interactions and none is coupled with a feasibility study of the use of biogas formed. This decoupling is partly the result of a very disciplinary approach. The EPI-H2 project aims to decipher and model the process leading to H2 production by integrating the functioning of individual cells and their interactions in mixed culture during a process, in order to validate the change of scale by integrating the feasibility of using the biogas produced. It is an interdisciplinary and innovative fundamental research project, with a continuum of studies ranging from integrated molecular metabolism to process scale, to propose an effective strategy for the development of a process that can eventually be valued for the production of renewable H2. It therefore requires to take advantage, in an integrated manner, several types of expertise and know-how: microbiology, metabolism, chemistry, modelling, process engineering in order to remove the scientific obstacles that limit the development and use of biotechnology. The project therefore aims to (i) decipher the bacterial communication within a synthetic consortium, (ii) estimate the impact of this one on the metabolism of the consortium's bacteria, in particular on the H2 production through a metabolic modelling approach that integrates experimental data from kinetic, metabolic and transcriptomic monitoring; (iii) evaluate the impact of scaling up on H2 production by a continuous process; and iv) validate the supply of an enzymatic fuel cell with the H2 produced, not purified. By integrating all fundamental knowledge, the ambition is to propose relevant parameters to contribute to the change of scale of the process, an essential step in the development of medium / long term applications.