MéLISSA STRAGIOTTI¹, CLAIRE LE BAYON², PILAR JUNIER<sup>1

1</sup>Laboratory of Microbiology, University of Neuchâtel, Switzerland. , ²Laboratory of Functional Ecology, University of Neuchâtel, Switzerland

Interactions between microorganisms and earthworms are known under the theory dubbed the Sleeping Beauty Paradox. In this theory, earthworms have developed a mutualistic interaction with soil microbiota. The intestinal mucus of earthworms activates microbial communities usually present in soil in a dormant state. This soil microbiota digests organic matter, making it available to the earthworm. Consequently, earthworms play a role in the regulation of the abundance and the diversity of microbial communities. However, one aspect that is poorly understood is the role of earthworms in the active dispersal of microorganisms. Soil is a heterogeneous habitat, particularly in the distribution of resources. Faced with nutrient depletion or other environmental stressors, some bacteria have the ability to form endospores, which are differentiated cells in a dormant metabolic state. Endospores are poorly mobile and thus their dispersal might be limited. However, their resistance might offer a way to reverse this, by dispersing within the intestinal tract of earthworms. In such context, the purpose of this research is to study the influence of the epigeic earthworms Eisenia fetida on the metabolic state of the endospore-forming bacteria Bacillus subtilis and its role in the active dispersal of this bacterium. We hypothesize that 1) B. subtilis endospores survive through the digestive tract of earthworm and germinate in its casts and 2) B. subtilis are spread by E. fetida. In order to address the first hypothesis, microcosms will be inoculated with GFP-labelled B. subtilis strains. Cultural methods will be used to quantify the microbial load of earthworms’ digestive content. In order to verify the second hypothesis, earthworms fed on a substrate inoculated with bacteria will be introduced in microcosms free of the studied strains. Microcosms will be harvested and the bacteria quantified as previously described. This study contributes to the understanding of soil functioning and microbial spatial distribution in soils and the role of earthworms as a vector of colonisation of new ecological niches by microorganisms.