Communal efforts, such as biofilm formation, make survival of individual organisms more likely. Organisms colonizing the phylosphere face abiotic and biotic pressure e.g. by highly fluctuating moisture or microbe immission. Bacterial biofilms have been extensively studied, however there is hardly any knowledge on eukaryotic biofilm formation and its impact on pathogen virulence or persistence on plants. Our goal within CEPLAS is to investigate mechanisms of mutualistic microbe-microbe interactions, shaping the foliar microbiome and their impact on plant growth and plant health.