Plastics debris pervades in our oceans and freshwater systems at an increasing accumulation rate. While identifying the major sources of plastics are critical, greater investigations on the plastic microbiome to characterize the whole microbial communities and putative plastic-degraders appear also essential. The major aim of MycoPLAST is thus to address the problematic of the fate of marine plastic litter which appears particularly relevant to the CES 04 “Scientific and technological innovations to support the ecological transition” as we will highlight specific microbial communities able to degrade plastics. The MycoPLAST proposal fits well with the CES associated keywords “bioremediation”, “ecological engineering”, “pollutant treatment”, “treatment of waste” and “pollution of waters”. In recent years, evidence has accumulated for the presence and activity of fungal communities in a wide variety of aquatic habitats. While numerous studies have provided evidence for metabolically active marine fungi, the extent to which they make a significant contribution to biogeochemical cycling of compounds, including pollutants, is still unknown. The overall aims of this proposal are to assess the diversity, activity and distribution of fungi associated with marine plastic debris samples and to evaluate, and possibly unleash, their ability to degrade complex plastic polymers. This will be achieved (i) by providing detailed information on the identity and environmental significance of fungi associated to a wide variety of plastic samples (retrieved from different aquatic habitats) using molecular marker gene analyses, (ii) by establishing an extensive collection of fungal isolates and by determining their ability to efficiently degrade plastic polymers, and (iii) by optimizing the utilization/degradation yield through microbial consortia, use of surfactants and constrained adaptation through iterative culturing. Our main hypothesis is that marine fungal communities represent an overlooked and untapped microbial component associated with marine plastic waste and that a better knowledge of their diversity, activity, functions and the exploration of their potential ability to degrade complex plastics could lead to efficient bioremediation applications in the current context of global threat to the planet and its inhabitants. Noteworthy, in addition to the access to a large collection of plastic samples from different marine locations, the proposed project will take advantage of a funded Tara Expedition starting in May 2019 for a “Tour of Europe”. During this expedition, having for theme ocean research and the preservation of the Ocean in the face of plastic pollution, “fresh” plastic samples (meso, micro and nanoplastics) will be collected and will also be accessible to the MycoPLAST project. The limited but nevertheless encouraging studies on these specific microorganisms clearly highlight the interest of this research topic, allowing to consider that the MycoPLAST project is highly original and will definitely lead to scientific breakthroughs and can be a first step towards standardized bioremediation approaches lowering plastic pollution in the Ocean through the bio-stimulation of specific marine microbial degraders.