**5. Conclusions**

Detritivorous earthworms interact intensively with microorganisms during vermicomposting, thus accelerating the stabilization of organic matter and greatly modifying its physical and biochemical properties. Digestion of the ingested material is the first step in earthworm-microorganism interactions. Passage of organic material through the gut of epigeic earthworms reduced the viable microbial biomass and affected the abundance of bacteria to a greater extent than fungi. Microbial activity also decreased after transit of the microorganisms through the earthworm gut. Accordingly, the presence of earthworms reduced microbial biomass and activity after the active phase of vermicomposting, although this effect depended on the earthworm species involved. The bacterial growth rate also decreased in the substrate, whereas the fungal growth rate was not affected after one month. The speed at which these transformations occurred made the active phase of vermicomposting a suitable stage for studying the relationships between earthworms and microorganisms and permitted us to understand the chemical and biological consequences of earthworm activities. Ultimately, these findings provide valuable information for the understanding of the transformations that organic matter undergoes during vermicomposting and, in addition constitute a powerful tool for the development of strategies leading to a more efficient process for the disposal and/or management of organic wastes.
