Bacterial Communities and Tetracycline Resistance Genes in the Soil-Rice Continuum Upon Tetracycline Exposure

Edible plants are known as key vectors for transmission of antibiotic resistance genes (ARGs) to humans. However, little is known about how antibiotic exposure affects the abundance of ARGs in the soil-rice continuum. This study assessed tetracycline (TC) content, tetracycline resistance genes (TRGs), class 1 integron-integrase gene (intI1), and bacterial communities in the mature soil-rice continuum exposed to varying concentrations of TC (0, 50, 100, and 300 ppm). As TC exposure levels increased, the TC content in rhizosphere soils and roots increased accordingly. However, TC residue was not detected in the grains. Additionally, sample type (rhizosphere soils, roots, and grains) was the key determinant of bacterial communities and TRGs profiles in the soil-rice continuum. The bacterial communities and TRGs profiles in the rhizosphere soils and roots exposed to TC >50 ppm were more dissimilar to those without TC than to those exposed to TC <50 ppm. The abundance of TRGs in the soil-rice continuum increased with the TC concentrations but declined when TC > 50 ppm. This decline was primarily due to changes in the abundance of tetX and tetZ. Variation partitioning analysis revealed that the TRGs profiles in rhizosphere soils is strongly affected by bacterial communities. In contrast, the variation in TRGs profiles in roots was predominantly explained by bacterial communities-TC interactions. However, the changes in TRGs profiles of grains could not be attributed to the bacterial communities, TC, or intI1. This study provides valuable insights into the response of TRGs profiles in the soil-rice continuum to TC exposure.