Response and mechanisms of the performance and fate of antibiotic resistance genes to nano-magnetite during anaerobic digestion of swine manure

Swine manure is an important reservoir of environmental antibiotic resistance genes (ARGs), and anaerobic digestion (AD) is a commonly used method for swine manure treatment. In this study, the optimized dosage of nano-magnetite to enhance methane production was figured out, the changes of the fate of ARGs response to nano-magnetite were investigated, and the microbial mechanisms were deciphered through the microbial community analysis and key functional genes quantification. Results showed that nano-magnetite could improve the methane production by maximum 6.0%, the maximum daily methane production could be increased by 47.8%, and the AD time could be shortened by above 20.0% at the addition of 75 mmol. The improved performance could be associated with the enhancement of direct interspecies electron transfer (DIET) and the inhibition release due to the formation of Fe-S precipitation not the nutrition elements role of nano-magnetite, and nano-magnetite did not significantly influence the dynamics of microbial community. Nano-magnetite could enhance the methanogenesis instead of the acetogenesis reflected by the functional genes analysis, and the limited effects of nano-magnetite on the fate of ARGs could be associated with its limited influence on the microbial community which determined the fate of ARGs during AD of swine manure.