Abstract: The intestinal contents from the foregut, midgut and hindgut of earthworms (Eisenia fetida) were collected under initial-starvation-cow dung continuous culture conditions, and the 16S rRNA gene amplicon sequencing was consequently conducted to investigate the segmental differentiation of gut bacterial communities and their responses to starvation and feeding. The results show that the bacterial community diversity and composition were similar between adjacent intestinal segments; the community similarity between midgut and hindgut segments was higher than that between foregut and midgut segments, and the differences were greater between separated gut segments (foregut vs. hindgut). The dominant bacterial phyla across all earthworm gut segments were Firmicutes (14%-55%), Actinobacteria (16%-39%), and Proteobacteria (15%-37%). The changing trends of dominant bacteria along with the gut transmission (foregut-midgut-hindgut) were inconsistent under different culture conditions. The core ASVs of the foregut, midgut and hindgut segments mainly belonged to Firmicutes (35%-48%), Actinobacteria (20%-26%), and gamma-Proteobacteria (14%-16%). The foregut and hindgut segments had unique core ASVs, which mainly belonged to delta-Proteobacteria (7%) and Fibrobacteres (6%), respectively. From initial state to starvation state, the Shannon diversity index of gut microbiota decreased significantly (P<0.05), while the Sobs richness index decreased insignificantly (P>0.05); the relative abundances of alpha-/delta-Proteobacteria and Actinobacteria decreased significantly (P<0.05), while that of gamma-Proteobacteria, Firmicutes and Bacteroidetes increased significantly (P<0.05). From starvation state to cow dung culture state, the Shannon diversity index and Sobs richness index further significantly decreased (P<0.05). The relative abundance of delta-Proteobacteria and Firmicutes increased significantly (P<0.05), while that of gamma-/alpha-Proteobacteria and Actinobacteria significantly decreased (P<0.05), and that of Bacteroidetes had no significant change (P>0.05). The cluster analysis results show that the gut microbiota of earthworms was stable to a certain extent. Combining the results of bacterial community structure and differential ASVs analysis, it was shown that starvation-cow dung culture changed the gut bacterial community of earthworms, with starvation mainly changing the bacterial community abundance, while cow dung culture changing both the bacterial community abundance and composition. Taken together, the intestinal microbial community of earthworms had obvious intestinal segment differentiation, which can resist disturbance and maintain stability to a certain extent. The earthworm gut microbial community displayed a clear response to both starvation and feeding, with a stronger response to feeding.

Key words: earthworm, gut microorganism, gut segment, starvation, cow dung, bacterial community