Effects of Copper Addition on Copper Resistance, Antibiotic Resistance Genes, and intl1 during Swine Manure Composting Original paper

What was studied?

The study examined the effects of copper addition during the composting of swine manure, specifically focusing on its impact on copper resistance genes (CRGs), antibiotic resistance genes (ARGs), and the integrase gene (intI1) that plays a role in horizontal gene transfer. Researchers evaluated how varying copper concentrations influenced the persistence and abundance of these genes in relation to the microbial community composition throughout the composting process. The research aimed to understand the interactions between copper exposure, resistance gene dynamics, and bacterial community shifts during composting, with an emphasis on environmental and microbiological factors.

Who was studied?

The study utilized swine manure as the primary substrate for composting, collected from a medium-sized farm in Yangling, China. The swine feed had been supplemented with trace elements like copper and antibiotics, ensuring that the manure had a baseline concentration of copper and resistance genes. The composting process was controlled in a laboratory setting, with specific concentrations of copper (200 mg/kg and 2000 mg/kg) added to simulate varying levels of environmental copper contamination. Through this setup, the study sought to understand the response of the manure’s microbial community, particularly the abundance and co-occurrence of copper and antibiotic resistance genes, as well as the intI1 gene.

Most important findings

The results demonstrated significant changes in the abundance of CRGs, ARGs, and intI1 throughout the composting process. The abundance of copper resistance genes such as pcoA and tcrB decreased, while genes like copA and cusA increased, suggesting that copper exposure exerted selective pressure on certain bacterial populations, enhancing their resistance capabilities. The study also observed that higher copper concentrations (Cu2000) had a more persistent effect on the microbial community composition, maintaining higher levels of certain CRGs even at later stages of composting. The presence of antibiotics, particularly macrolides, co-selected for the persistence of these resistance genes, as evidenced by the enhanced abundance of erm(A) and erm(B) genes, which are associated with macrolide resistance. Network analysis revealed that these genes, particularly the copper and antibiotic resistance genes, were co-located on the same bacterial taxa, such as Steroidobacter and Corynebacterium, suggesting these bacteria as potential hosts for the genes.

Key implications

The study highlights the interconnectedness between copper resistance, antibiotic resistance, and gene transfer during the composting process. The findings underscore the role of composting as a potential pathway for the persistence and spread of these resistance genes in the environment, especially in agricultural settings. The research suggests that copper, especially at higher concentrations, can alter the microbial community structure and potentially facilitate the horizontal transfer of resistance genes, which could have implications for public health and the management of antibiotic resistance in the environment. Understanding these dynamics is critical for developing strategies to mitigate the spread of resistance genes in composted manure, which is commonly applied to soil.