Interaction of arsenic biotransformation genes, microorganisms and antibiotic resistance genes during pig manure composting

Arsenic (As) pollution and antibiotic resistance genes (ARGs) pollution in livestock manure compost have been studied much, but the interaction between the two has been studied very little. Therefore, five kinds of As addition experiments of pig manure composting were set up in this study: T1 (control group, no additive), T2 (sodium arsenate 10 mg/kg), T3 (sodium arsenate 20 mg/kg), T4 (saroxyarsenic 10 mg/kg) and T5 (saroxyarsenic 20 mg/kg). The interaction of ARGs, As biotransformation genes (ABGs), microbial communities and their metabolic functions during composting were studied, using smart chip real-time PCR, high-throughput fluorescent quantitative PCR and high-throughput sequencing. The results showed that the addition of exogenous arsenic increased the temperature, inhibited the degradation of organic matter, and increased the ratio of humic acid to fulvic acid. Organic arsenic stimulated more ABGs production, while inorganic arsenic induced more ARGs production. The effect of arsenic addition on microbial community was significant. The effect of inorganic arsenic on microbial community was faster (about 20 days), while the effect of organic arsenic required a certain transformation (60 days). Both kinds of exogenous arsenic increased the relative abundance of Firmicutes, but had different effects on other bacteria groups. At the same time, the metabolic genes of microorganisms were also affected in different degrees by As addition. Through RDA analysis and network co-occurrence, it can be seen that the contribution rates of Firmicutes and Bacteroidota to the change of ARGs were 15.6% and 18.7% respectively, and the contribution rates of water content and organic matter content to the change of ARGs were 18.7% and 12.1% respectively. In addition, ABGs and ARGs have some positive correlations. The results of this study will help to clarify the internal interaction mechanism between complex pollutants.