Earthworms drastically change fungal and bacterial communities during vermicomposting of sewage sludge

Wastewater treatment plants produce hundreds of million tons of sewage sludge every year all over the world. Vermicomposting is well established worldwide and has been successful in processing sewage sludge, which can contribute to alleviate the severe environmental problems caused by their disposal. Here, we utilized 16S and ITS rRNA high-throughput sequencing to characterize bacterial and fungal community composition and structure during the gut- and cast-associated processes (GAP and CAP, respectively) of vermicomposting of sewage sludge. Bacterial and fungal community composition and diversity changed significantly during both vermicomposting processes. Most of the bacterial and fungal taxa in the sewage sludge were eliminated during vermicomposting, mainly through the GAP. Vermicomposting of sewage resulted in a stable and rich microbial community with potential biostimulant properties that may aid plant growth. Our results support the use of vermicompost derived from sewage sludge for sustainable agricultural practices.