Differences in the Structure and Function of the Gut Microbiota of the Earthworm (Amynthas aspergillum) Under Different Habitat Conditions

This study aims to explore the shaping mechanism of habitat heterogeneity on its gut microecology and to clarify the structural differences and functional succession patterns of gut microbiota of an earthworm Amynthas aspergillum under artificial breeding versus natural habitats. A total of 175 A. aspergillum specimens and their corresponding soil samples were collected from seven typical habitats in Guangxi: fertile farmland, barren farmland, plantation forest, primary forest, artificial grassland, wasteland slope, and a breeding farm. 16S rRNA high-throughput sequencing was employed to analyze the gut microbiota structure. PICRUSt2 was used to predict metabolic functions, and the correlation between soil physicochemical factors and community characteristics was analyzed. There were only 25 core shared OTUs found across the seven habitats, indicating a strong habitat specificity of the gut microbiota in A. aspergillum. The fertile farmland group exhibited the highest species richness (Chao1) and diversity (Shannon) among all groups (p < 0.05). Although rich in organic matter, the breeding farm group showed the highest Simpson dominance index. Actinomycetota, Pseudomonadota, Chloroflexota, and Bacillota were the dominant shared phyla in all groups. LEfSe analysis revealed that the wasteland slope habitat specifically enriched the stress-tolerant genus Mycobacterium, while the breeding farm was dominated by the anaerobic fermentation-capable genus Clostridium. Functional prediction indicated that the primary forest group had the most complex microbial metabolic network, while the breeding farm group exhibited a “functional simplification” trend focused on basic carbohydrate metabolism, which was significantly correlated with the soil C/N ratio. Soil physicochemical factors, particularly the intensity of anthropogenic disturbance and the composition of organic matter, are the key forces driving the assembly of A. aspergillum gut microbiota through environmental filtering. Artificial monoculture breeding leads to the functional degradation of the gut microecology.