Abstract
Earthworms are crucial to soil ecosystems as keystone species.They perform various ecological functions through their associated microbiomes.However,the characteristics of these microbiomes in various vermicompartments(earthworm-associated compartments)within soil-earthworm systems have not been systematically studied.Here,using earthworms of two ecotypes(i.e.,epigeic Eisenia fetida and anecic Metaphire guillelmi)as models,we conducted a full and comprehensive exploration of the bacterial community in several potential distinct compartments,including bulk soil,drilosphere,gut wall,gut content,and casts,through 2D-terraria incubation technology and high-throughput sequencing approaches.Bacterial diversity,community structures in each compartment,differential OTUs in vermicompartments compared with bulk soil,and the co-occurrence relationship of bacteria in bulk soil and gut-compartments(i.e.,gut wall and gut content)were assessed.Results showed that three major vermicompartments,i.e.,drilosphere,gut,and casts,were distinctly different in hosting the bacterial community.The levels of alpha diversity followed the order of drilosphere＞casts＞gut wall ≈ gut content.These patterns of vermicompartments along earthworms did not vary with ecotype,implying that the vermicompartments were the primary factors influencing the bacterial community.Finally,based on the difference in microbiomes in gut-compartments and the state-of-the-art use of the term"gut microbiomes",it is recommended to establish a unified definition of gut microbes that encompasses microbiomes residing in both the gut wall and gut content,which could provide a clear and consistent understanding of gut microbiomes.This work provides a comprehensive overview of earthworm-associated microbiomes,enhancing our understanding of fundamental earthworm ecology and soil biology.
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