Effects of tetracycline residuals on humification, microbial profile and antibiotic resistance genes during vermicomposting of dewatered sludge.

Vermicomposting is a green technology used in the recycling of sewage sludge using the joint action of earthworms and microorganisms. Although tetracycline is present in abundance in sewage sludge, little attention has been given to its influence on vermicomposts. This study investigated the effects of different tetracycline concentrations (0, 100, 500 and 1000 mg/kg) on the decomposition of organic matter, microbial community and antibiotic resistance genes (ARGs) during vermicomposting of spiked sludge. The results showed that 100 mg/kg tetracycline could stimulate earthworms' growth, accompanied by the highest humification and decomposition rates of organic matter in the sludge. The abundance of active microbial cells and diversity decreased with the increase in tetracycline concentrations. The member of Bacteroidetes dominated in the tetracycline spiked treatments, especially in the higher concentration treatments. Compared to its counterparts, the addition of tetracycline significantly increased the abundances of ARGs (tetC, tetM, tetX, tetG and tetW) and Class 1 integron (int-1) by 4.7-186.9 folds and 4.25 folds, respectively. The genera of Bacillus and Mycobacterium were the possible bacterial pathogen hosts of ARGs enriched in tetracycline added group. This study suggests that higher concentration of tetracycline residual can modify microbial communities and increase the dissemination risk of ARGs for final sludge vermicompost.