Elucidating the beneficial effects of diatomite for reducing abundances of antibiotic resistance genes during swine manure composting

Abstract

Diatomite (DE) has been used for nitrogen conservation during the composting of feces but its effects on antibiotic resistance genes (ARGs) and the associated mechanisms are still unclear. In this study, DE was added at three different proportions (0%, 4%, and 8%) to swine manure during composting. The results showed that adding DE helped to reduce the abundances of ARGs and the maximum decrease (88.99%) occurred with the highest dose. DE amendment promoted the transformation of reducible copper into a more stable form, i.e., the residual fraction, which reduced the selective pressure imposed by copper and further decreased the abundances of ARGs. Tn916/1545 and intI1 were critical genetic components related to ARGs, and thus the reductions in the abundances of ARGs may be attributed to the suppression of horizontal transfer due to the decreased abundances of mobile genetic elements (MGEs). The microbial community structure (bacterial abundance and diversity) played key role in the evolution of ARGs. DE could enhance the competition between hosts and non-hosts of ARGs by increasing the bacterial community diversity. Compared with CK, DE amendment optimized the bacterial community by reducing the abundances of the potential hosts of ARGs and pathogens such as Corynebacterium, thereby improving the safety of the compost product. In addition, KEGG function predictions revealed that adding DE inhibited the metabolic pathway and genes related to ARGs. Thus, composting with 8% DE can reduce the risk of ARG transmission and improve the practical value for agronomic applications.