Distribution Pattern of Genes Conferring Resistance to Macrolides in Rhizosphere Soil of Maize

Antibiotic residues in crop soils create selection pressure on the occurrence and dissemination of antibiotic resistance genes (ARGs), rendering rhizosphere soils "hot spots" for ARGs. In the present study, the soil microbiome was monitored for macrolide resistance genes (erms) arising from the rhizosphere in maize during different crop growth periods over a duration of 63 days using real-time polymerase chain reaction (PCR) technology. The relative abundance (erms :16S rDNA) of erms in the soil was in the order of ermF > ermX > ermB > ermC. The relative abundance of ermF, ermX, ermB, and ermC in bulk soil were 4.72×10^-2, 1.98×10^-3, 7.13×10^-1, and 1.75×10^-2, respectively, on D7, whereas, on D63, the relative abundance were 1.74×10^-3, 3.24×10^-4, 3.53×10^-3 and 2.28×10^-3, respectively. The corresponding gene proliferation rates in bulk soil were -96.3%, -83.6%, -99.5%, and -87.0%, respectively, compared to -88.3%, 103.0%, -88.6%, and 71.5%, respectively, in rhizosphere soil. These results suggest that the maize rhizosphere had a significant effect on the proliferation or transfer of ermC and ermX. The relative abundance of erms at different soil depths was in the order of 0-0.2, > 0.2-0.4, and > 0.4-0.6 m, indicating that the resistance genes had a downward migration tendency, with relative abundance of resistance genes decreasing with an increase in soil depth. The detection rate of resistance genes at corresponding depths of soil for the same sample was in the order of RH > CK, suggesting that the presence of the plant rhizosphere not only promotes an increase in resistance gene abundance in the soil but also promotes vertical migration in the soil profile.