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Antibiotics and heavy metals added to livestock and poultry feed are excreted in manure, which is added to agricultural soil and causes severe pollution. However, the effects of oxytetracycline (OTC) and zinc (Zn), which are present at relatively high levels in feed additives, on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and microbial communities have not been comprehensively studied. This study evaluated the effects of OTC and Zn on environmental factors, microorganisms, MGEs, and ARGs. The expression of MGEs in soil was stimulated by adding Zn at concentrations of 500 and 1000 mg/kg or OTC at concentrations of 30 and 100 mg/kg; however, the addition of their combination hindered the expression of MGEs in soil. The abundance of total MGEs and ARGs tended to decrease with increasing concentrations of Zn and OTC and the number of incubation days. Low and high OTC concentrations strongly inhibited sul and tet resistance genes, respectively. Network analysis showed that changes in the population of Firmicutes and Proteobacteria had the greatest impact on ARG abundance. Redundancy analysis revealed that MGEs, particularly intI2 , facilitated the transfer and spread of ARGs and had the greatest impact on changes in ARG abundance. These findings provide reference values for the prevention and resolution of ecological and environmental risks posed by the presence of Zn and OTC in organic manure soil. [Display omitted] • Zn and OTC contamination alone promoted the expression of MGEs (intI1 and intI2). • ARGs expression was reduced by contamination with high Zn and OTC concentrations. • Firmicutes and Proteobacteria are the main potential host bacteria of ARGs. • MGEs (especially intI2) play a key role in the expression and propagation of ARGs. [ABSTRACT FROM AUTHOR]

Sewage treatment plants are known as repositories of antibiotic resistance genes (ARGs). Adding biochar and inoculating with exogenous microbial agents are common ways to improve the quality of compost. However, little is known about the effects of these exogenous additives on the fate of ARGs during composting and the related mechanisms. In this study, municipal sludge was taken as the research object to study the ARG-removal effects of four composting methods: ordinary compost (CT), compost with hyperthermophiles (HT), compost with hyperthermophiles and 2.0% biochar (HT2C) and compost with hyperthermophiles and 5.0% biochar (HT5C). Real-time quantitative PCR (qPCR) and 16S rRNA high-throughput sequencing were conducted to analyze the ARGs, MGEs and bacterial community. After composting, the abundance of ARGs in CT was reduced by 72.7%, while HT, HT2C and HT5C were reduced by 80.7%, 84.3% and 84.8%, respectively. Treatments with different proportions of biochar added (HT2C, HT5C) had no significant effect on the abundance of ARGs. Network analysis showed that Firmicutes and Nitrospirae were positively associated with most ARGs and may be potential hosts for them. In addition, redundancy analysis further showed that the class 1 integrase gene (intI1), pH and organic carbon had a greater effect on ARGs. Our findings suggested that the combination of hyperthermophiles and biochar during the composting process was an effective way to control ARGs and mobile genetic elements (MGEs), thus inhibiting the spread and diffusion of ARGs in the environment and improving the efficiency of treating human and animal diseases. [ABSTRACT FROM AUTHOR]

With rapid developments in livestock and poultry farming, antibiotics and heavy metals are entering the soil environment as feed additives. However, their relationships with antibiotic resistance genes (ARGs), microorganisms, and environmental factors are unclear. In this study, cadmium (Cd) and sulfadiazine (SD) were selected as representative heavy metal and antibiotic substances, respectively, to investigate the relationships among environmental factors, microorganisms, mobile genetic elements (MGEs), and ARGs. Addition of Cd and SD, both individually and in combination, increased the abundances of total ARGs and MGEs. The abundance of total ARGs increased by 0.89-fold and 1.06-fold in C2 and C8 (only-Cd-added groups), 1.61-fold and 6.53-fold in S10 and S100 (only-SD-added groups), and 7.29-fold, 7.62-fold, 2.32-fold, and 6.80-fold in C2S10, C2S100, C8S10, and C8S100 (groups with Cd and SD in combinations), respectively. Proteobacteria and Bacteroidetes were the most abundant bacterial phyla. MGEs (especially intI1) had the greatest impact on ARGs and played a crucial role in their propagation and expression. Exploring the effects of heavy metals and antibiotics in soil on ARGs is important for comprehensively assessing their ecological and environmental risks to ARGs. [Display omitted] [ABSTRACT FROM AUTHOR]