Insights into the earthworm gut multi-kingdom microbial communities.

Earthworms are widely known to impact soil health, having a key role in nutrient cycling and are often referred to as soil engineers. They are vital for soil microbial assemblages particularly through their feeding and burrowing activity in soil. Earthworms feed on soil organic matter and litter, and the resulting casts alter the soil microbial community. However, the gut microbiome of earthworms remains less known. In this study, we used amplicon sequencing of the 16S rRNA gene for bacteria and 18S rRNA gene for eukaryotes to assess the gut community assemblages of earthworm species within three genera Aporrectodea, Allolobophora and Lumbricus that represent different life forms sharing the same habitat. The objective was to compare the gut microbiome profiles of eukaryotic and prokaryotic organisms to assess significance of earthworm life forms, and to explore the cross kingdom networks in an attempt to identify keystone species. We found a high eukaryotic diversity with a dominance of the SAR supergroup along with fungi and metazoan in the earthworm gut. The bacterial community were dominated by members of Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, and Verrucomicrobia. The eukaryotic and prokaryotic communities showed similar differences in alpha diversity, being lowest in Lumbricus herculeus. The beta diversity showed earthworm species as a key factor in shaping gut microbiomes with L. herculeus harboring distinct microbiomes compared to species of Aporrectodea caliginosa, A. longa, A. tuberculata and Allolobophora chlorotica. Cross kingdom networks showed high interactions between several protist and bacterial OTUs. In conclusion, this study suggested that the community assemblages of gut microbiomes were shaped by earthworm species and life form, and such assemblage consists of cross kingdom interactions among eukaryotes and prokaryotes.