Aims: This work investigates how different soil concentrations of cadmium (Cd) and copper (Cu) affect bacterial community structure and bacterial antibiotic resistance genes (ARGs). Furthermore, we explored key environmental factors that influence ARGs expression, to identify effective approaches to mitigate the spread of antibiotic resistance within environment.
Methods: We established a soil microcosm experiment using soil containing different concentrations of Cu and Cd. The relative expression of ARGs in the soil bacteria was determined by quantitative polymerase chain reaction (qPCR) experiments. We performed genomic sequencing/16S rRNA sequencing using the Illumina MiSeq system to assess the bacterial diversity of soil samples.
Results: High concentrations of Cd and Cu contamination significantly increased the relative abundance of the ARGs, such as sul1, intl1, and blaVIM. The ARGs tetX and tetG were most sensitive to Cd, as their abundance significantly increased even at low concentrations of Cd. In addition, Cu and Cd clearly altered soil bacterial community structure. Overall, the change in bacterial diversity was more pronounced in response to Cu than to Cd. Correlation analysis and network analysis showed that ARGs detected in this study, such as sul1, tetX, tetM02, and blaVIM, were widely distributed across multiple bacterial phyla. Changes in ARG profiles were closely associated with variations in bacterial communities (e.g. Streptomyces, Bradyrhizobium, genus BIrii41 (Polyangiales), and Haliangium), which indicate that these genera are the potential hosts of these resistance genes.
Conclusion: Our work provides direct evidence that heavy metals like Cu and Cd may co-select for ARGs in soil bacterial communities, which poses a potential health risk to humans.