Opposite Effects of Planting on Antibiotic Resistomes\nin Rhizosphere Soil with Different Sulfamethoxazole Levels

Achieving consensus about the rhizosphere\neffect on soil antibiotic\nresistomes is challenging due to the variability in antibiotic concentrations,\nsources, and the elusory underlying mechanisms. Here, we characterized\nthe antibiotic resistomes in both the rhizosphere and bulk soils of\nsoybean plants grown in environments with varying levels of antibiotic\ncontamination, using sulfamethoxazole (SMX) as a model compound. We\nalso investigated the factors influencing resistome profiles. Soybean\ncultivation altered the structure of antibiotic-resistant genes (ARGs)\nand increased their absolute abundance. However, the rhizosphere effect\non the relative abundance of ARGs was dependent on SMX concentrations.\nAt low SMX levels, the rhizosphere effect was characterized by the\ninhibition of antibiotic-resistant bacteria (ARBs) and the promotion\nof sensitive bacteria. In contrast, at high SMX levels, the rhizosphere\npromoted the growth of ARBs and facilitated horizontal gene transfer\nof ARGs. This novel mechanism provides new insights into accurately\nassessing the rhizosphere effect on soil antibiotic resistomes.