Fitness reduction of antibiotic resistome by an extra carbon source during swine manure composting.

This study employed high-throughput quantitative polymerase chain reaction to evaluate the effects of specific co-substrate and additive on the fitness of antibiotic resistome during swine manure composting. The results showed that corncob particle as a co-substrate significantly reduced the relative abundances of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) simultaneously. The diversity of ARGs was also reduced more effectively by corncob addition. Brick granule as an additive reduced the concentrations of bioavailable Cu and Zn. However, the relative abundances of ARGs and MGEs were not reduced by the addition of brick granule subsequently. Redundancy analysis indicated a negative effect of the C content and positive effects of class I integrase gene (intI) and bioavailable metals on the variation of the relative abundance of ARGs (p < 0.01). The Procrustes test showed a higher goodness-of-fit between the relative abundance of ARGs and 16S rRNA genes (r = 0.8166; p < 0.0001). Our results suggests that the effect of corncob particle on the relative abundance of ARGs was achieved by driving the changes in physicochemical properties and microbial communities. This study confirmed the hypothesis of fitness cost and demonstrated the contribution of extra C source to ARG attenuation during composting.