Impacts of earthworm introduction and cadmium on microbial communities composition and function in soil

Heavy metal contamination of soil has become a public concern. Earthworms are key players in the functioning and service of soil ecosystems, with comprehension of their introduction in the polluted soil offering new insights into the protection of soil resources. In the present study, we evaluated the effects of earthworm (Eisenia fetida) introduction and Cd (0, 10, 30, and 60 mg kg^-1 of Cd) exposure upon soil microbial community using 16S rRNA gene amplicon sequencing. Our research demonstrated that Gemmatimonadetes and Deinococcus-Thermus upregulated significantly, while Chryseolinea showed an obvious decreasing trend after earthworm introduction. In Cd contaminated soil, many genera exhibited a greater presence of Cd-dependent bacteria, namely Cd-tolerant bacteria such as Altererythrobacter and Luteimonas, and a decrease of sensitive bacteria, such as Amaricoccus and Haliangium. Moreover, functional prediction analysis of soil microbiota indicated that earthworm introduction and Cd exposure changed functional pathways of soil microorganisms. The results obtained in this study are beneficial for understanding soil microbial community impacted by earthworm, and for exploring Cd resistant or tolerant bacteria, with potentially significant findings for soil biodiversity and Cd bioremediation.