The project aims at discovering the fundamental principles governing the adaptation of multi-species communities to disturbance on a 4-species (4S) bacterial biofilm of natural origin. In the nature, these systems play a crucial role in the biogeochemical cycles of carbon, nitrogen and water. The disturbance of their balance can only come along with striking consequences at a global scale. However, we currently ignore how these communities will respond to climate change. The examination of this question at the natural ecosystem scale is hardly feasible due to the impossibility to rationally vary and control the environmental conditions. Besides the laboratory studies are mostly mono-species while it is increasingly becoming obvious that the inter-species interactions are crucial for the assembly and the development of these communities. To better understand the factors which support the adaptation of these communities to disturbances, we propose gathering biophysicists and microbiologists who will examine the global and molecular responses of the model 4S community to controlled environmental changes. In a first phase, we will build a quantitative phenotypic and genetic description of the 4S biofilm established in a microfluidic platform enabling to control the applied physical and chemical conditions as well as to monitor in real time the development of the community. Through a combinatorial approach — all biofilms from mono- to 4-species will be examined in parallel — we will first identify interspecies interactions and their environmental and genetic background in a reference state. Then, in a second phase, we will carry out the perturbation program consisting in completing series of controlled disturbances of various natures — chemical, physical and social — to detect characteristic adaptive trajectories (resistance, resilience or redundancy) and select remarkable time-points — climax or plateau — which will then be studied from a genetic point of view in the third phase. In this third phase, we will study the transcriptional and genomic alterations having occurred at the selected time points of the adaptive trajectory. Through this approach, we aim at identifying the genes and the interspecies interactions involved in the adaptation to a given perturbation, and isolate potentially emerging mutants. On the other hand, we will conduct a theoretical analysis to model the population dynamics induced by disturbances. This program holds several methodological and technological challenges such as the development of a quantitative method for describing the community phenotype, the development of the experiment automation required by the combinatorial approach and the disturbance screening step; as well the genetic analyses that will be performed in the multi-species context, thus needing the implementation of the latest technical advances in the field. Our approach aims at overcoming the difficulty in linking phenotypic and genetic information. Our strategy is to pre-select a limited number of relevant trajectories and to perform correlated analyses — phenotypic and genetic — on defined time points of the adaptive path to bring over adaptation mechanism features in this 4S adherent community. The completion of our program should provide a first clarification on the role of interspecies interactions in the specific architecture of the mixed community and its capacity to adapt to a given stress. We also expect other benefits such as the advance of new experimental tools to analyze adherent bacterial communities and new strategies to control bacterial biofilms, potentially new avenues to artificially assemble useful multispecies communities with defined function. Finally, our work will allow to evaluate the potential of multispecies simplified models, grown in the laboratory conditions for understanding and predicting the dynamics of natural systems.