Galdieria sulphuraria is a cosmopolitan photosynthetic microalga isolated in volcanic zones. This acidophilic and thermophilic alga is characterized by a high metabolic flexibility as well as by a high biomass productivity. G sulphuraria is able to grow in phototrophic regime (exclusive use of light as a source of energy), heterotrophy (fermentation or reduced carbon respiration) as well as in mixotrophic conditions (simultaneous use of light and reduced carbon). G. sulphuraria is considered as an emerging system for Biotech applications. On the other hand, the molecular bases of these unique performances are still largely unknown. For this reason, we propose a project to understand the molecular mechanisms of Galdieria mixotrophic growth as a step towards achieving maximum biomass for biotechnological applications. This will be achieved by high-throughput screening (photosynthesis, growth) of different strains under photo / mixotrophic conditions. Comparative genomics, proteomics as well as metabolic analyses will make it possible to reconstruct in silico the metabolism of G. sulphuraria, thanks to a new bioinformatic tool designed for detailed reconstruction and visualization and system-wide analyses of metabolic networks. This will make it possible to carry out metabolic modelling as well as flux balance analysis, and thus to identify the constraints and the limiting steps in the conversion of light and carbon sources. To achieve these goals, we have assembled a consortium of three partners (LPCV, HHU, BGE) with a solid record in the study of the metabolism of photosynthetic organisms, all leaders of research in their scientific fields. The partner laboratories contributed to the first studies of G. sulphuraria (HHU), including the sequencing of its genome, and the identification of the mechanism of mixotrophy in microalgae (LPCV). The three partners will study the key steps of mixotrophic metabolism with complementary methodological expertise (LPCV: physiology, respiration and metabolic reconstruction; BGE: proteomics, bioinformatics; HHU: comparative genomics and metabolic fluxes). This project will provide knowledge on how to optimize the productivity of this alga and will identify targets for improved biomass productivity in the perspective of future metabolic engineering.