Émergence de la diversité en tant que réponse à la compétition intra-spécifique au sein des biofilms mixtes de Pseudomonas putida

International audience; In natural and man-made environments, biofilms are known to be complex associations of microorganisms which development is controlled by a network of bacterial interactions. As biofilm is a dynamic environment, these interactions evolve over time, often illustrating the adaptation of the whole bacterial community to its environmental conditions on one hand and of the bacterial community members to each other on the other hand. From this process the structure and the functional properties of the whole biofilm finally emerges. Genetic diversification and selection of variants with increased fitness in the conditions experienced is one of the known mechanisms enabling the adaptation of species to the biofilm way of life. Therefore, a better understanding of the emergence of this genetic diversity and overall the dynamic mechanisms of adaptation of bacterial species in biofilm is thus a first step towards the managing of ecosystem functions and evolution. In this aim, we focused in this work on the adaptation of the model strain Pseudomonas putida KT2440 (GFP-tagged) in mixed biofilm with another strain from the same species (P. putida mCherry-tagged) more recently isolated from roots of plants. We first analysed the emergence of colony morphology variants of Pseudomonas putida KT2440 GFP in pure culture or in mixed biofilms with the P. putida mCherry strain. Three colonies variants of P. putida KT2440 GFP (2000 colonies screened) were obtained from the mixed biofilm of both P. putida strains after 168h of growth whereas no variant was identified from the axenic P. putida KT2440 biofilm on the basis of colony morphology. The three variants were then phenotypically characterized (growth rate, cell surface properties, swimming, swarming, macrocolonies) and their ability to form biofilms alone or with the P. putida mCherry strain was analysed using 3D confocal microscopy. Variants exhibited distinct phenotypes and produced biofilm with specific architecture in comparison with the ancestor. In the mixed biofilms, KT2440 variants also better competed with the P. putida mCherry strain compared to the ancestor. Mixed biofilms of 2 or the 3 variants and ancestor with the P. putida mCherry strain are currently under evaluation to highlight potential synergistic effect resulting from the strain association. To sum up, this work provides evidence that an intra-specific competition can foster the emergence of phenotypic diversification which might increase the global fitness of the resulting population and highlights the importance of bacterial interactions in the evolution and adaptation of microbial communities.