摘要
      抗生素耐药性细菌和抗生素耐药性基因（ARGs）的传播对人类和兽医健康构成严重风险。虽然许多研究都集中在活的抗生素耐药性细菌向环境的迁移上，但尚不清楚死细胞中的细胞外ARG（eARGs）是否可以转移到活细菌中，以促进自然界抗生素耐药性的进化。在这里，我们使用来自死亡的、抗生素抗性的斯氏假单胞菌细胞的eARGs，通过自然转化（一种涉及eARGs基因组整合的水平基因转移机制）来跟踪eARGs向活的斯氏普氏假单胞杆菌细胞的移动。在无菌、不含抗生素的农业土壤中，我们控制了eARG的浓度、土壤湿度和与eARGs的接近程度。我们发现，在只接种0.25的土壤中发生了转化 μg的eDNA g−1土壤，表明即使是低浓度的土壤eDNA也可以促进转化（之前的估计值为2~40 μg eDNA g−1土壤）。当eDNA增加到5时 μg g−1土壤中，耐抗生素的施氏疟原虫细胞数量增加了5倍。我们发现，eARGs在陆地系统典型的土壤湿度（5至30%重量含水量）下转化，但在非常高的土壤湿度下（>30%）被抑制。总的来说，这项工作表明，死亡细菌及其eARGs是一种被忽视的抗生素耐药性途径。更普遍地说，eARGs在无抗生素土壤中的传播表明，在没有抗生素选择的情况下，转化可以建立遗传变异，土壤环境在调节转化中发挥着关键作用。
ABSTRACT
Antibiotic-resistant bacteria and the spread of antibiotic resistance genes (ARGs) pose a serious risk to human and veterinary health. While many studies focus on the movement of live antibiotic-resistant bacteria to the environment, it is unclear whether extracellular ARGs (eARGs) from dead cells can transfer to live bacteria to facilitate the evolution of antibiotic resistance in nature. Here, we use eARGs from dead, antibiotic-resistant Pseudomonas stutzeri cells to track the movement of eARGs to live P. stutzeri cells via natural transformation, a mechanism of horizontal gene transfer involving the genomic integration of eARGs. In sterile, antibiotic-free agricultural soil, we manipulated the eARG concentration, soil moisture, and proximity to eARGs. We found that transformation occurred in soils inoculated with just 0.25 μg of eDNA g−1 soil, indicating that even low concentrations of soil eDNA can facilitate transformation (previous estimates suggested ∼2 to 40 μg eDNA g−1 soil). When eDNA was increased to 5 μg g−1 soil, there was a 5-fold increase in the number of antibiotic-resistant P. stutzeri cells. We found that eARGs were transformed under soil moistures typical of terrestrial systems (5 to 30% gravimetric water content) but inhibited at very high soil moistures (>30%). Overall, this work demonstrates that dead bacteria and their eARGs are an overlooked path to antibiotic resistance. More generally, the spread of eARGs in antibiotic-free soil suggests that transformation allows genetic variants to establish in the absence of antibiotic selection and that the soil environment plays a critical role in regulating transformation.

https://journals.asm.org/doi/full/10.1128/aem.02280-21?casa_token=WprWtMiYdA0AAAAA%3Ai8Bd-0S-7oiD1dF69CLZKa0ZPpo4eoEUNVER8gY1ihXyRrtQoGcG8lgiepn5WvUaffFFhBHSdmASuPE