Low amounts of chitin induce growth promotion of lettuce and strawberry, which is related to an altered microbial community in the peat substrate (PS) and the rhizosphere, the soil surrounding the plant root. I expect that this change in microbial community, and presumably the activation of key microbial species, is essential for chitin to be beneficial to crop production. However, it is still unknown who is “key” and how they induce the chitin-related plant growth promotion, which is probably linked to at least one of the following mechanisms: (1) the release of plant available N by chitin degradation; (2) the deacetylation of chitin to chitosan, a recognized plant growth promoter; (3) the activation of other microbial mechanisms related to growth promotion. In this project, I aim to clarify the mode of action of chitin on plant growth promotion. Chitin degraders will be identified by combining stable isotope probing and metagenomics analyses. Next, chitin degradation will be quantified through a targeted metabolomics approach and metatranscriptomics. The data will finally be combined to select strains for which we will validate growth promotion and chitin-degrading capacities using various bioassays including a fast-screening tool I will develop to identify key microbial species/microbial enzymes in growing media which will help to predict the efficacy of chitin as a plant beneficial.