There is a wealth of microbial diversity in the environment, in soil, on plants, and in the atmosphere. Urbanisation usually involves disturbance and sealing of soil, along with a decrease and alteration of vegetation. This process drastically reduces natural microbial sources such as soil and phyllosphere (leaf surfaces), which also contribute to enriching the atmosphere. Nevertheless, in an urban environment, other microbial sources are more common, such as wastewater treatment, trash, and human-associated microbes. Significant differences have been observed in the environmental microbial communities between urban and non-urban environments. Several hypotheses highlight the importance of contact with diverse natural microbial communities for human health, especially for children. In this webinar, using a case study of the Belgian B@SEBALL project, we will illustrate how to investigate microbial biodiversity at school playgrounds and its potential contribution to different aspects of children’s health. This case study showcases the possibilities and limits of 16S rRNA amplicon sequencing in the context of the biodiversity hypothesis. Does microbial diversity benefit human health? The answer seems to be more nuanced than expected. We will also demonstrate the power of adjusting and generating hypotheses based on field microbiome data.You may either watch the entire presentation from the introduction or navigate directly to a specific section by clicking the links provided below:IntroductionCharacteristics of urban environments associated with urban diseasesThe human microbiome and its importanceMicrobiomes connecting One healthThe biodiversity hypothesisInvestigating the biodiversity hypothesis in Belgian schoolsQ&A