Antagonistic effects of Actinobacteria on fecal coliforms in sludge vermicomposting: Studies based on ecological and biochemical perspectives

Although actinobacteria play a crucial role in sludge vermicomposting, their succession dynamics and antagonistic mechanisms against pathogenic bacteria during vermicomposting process remain unclear. This study investigated the changes of actinobacterial communities and their antagonistic effects on fecal coliforms (FC) from ecological and biochemical perspectives by comparing sludge treatments with and without earthworm inoculation. Results showed that the addition of earthworms could lead to a significantly different degradation pathway of sludge. Compared to the control, the relative abundance and alpha diversity of actinobacteria in vermicomposting were significantly higher than those in control after 15 days (P < 0.05). Moreover, the number of FC in the vermicompost reduced by 70.72% against the control product (P < 0.001). The neutral community model and microbial network analysis revealed that actinobacteria combined with earthworms exhibited greater functionality and stability in the later stages than those in control, creating favorable conditions for the suppression of FC. In addition, three strains of the genus Streptomyces isolated from vermicompost exhibited significant antagonistic effects against FC, which exerted multi-level antibacterial mechanisms. This study suggests that the earthworms modulate actinobacterial community dynamics during sludge vermicomposting, thereby enhancing the secretion of antagonistic compounds from actinobacteria that effectively inhibit FC.