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Dead but not forgotten: how eDNA, moisture, and space modulate the horizontal transfer of extracellular antibiotic resistance genes in soil
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Description: Bacterial death can release extracellular antibiotic resistance genes (eARGs) into the environment. eARGs are abundant in agricultural soils, which may facilitate the movement of eARGs from dead to live bacteria through a mechanism of horizontal gene transfer called natural transformation. Here, we track the spread of eARGs from dead, antibiotic-resistant Pseudomonas stutzeri to live antibiotic-susceptible P. stutzeri in sterile agricultural soil. Transformation increased with the abundance of eARGs and occurred in soils ranging from 5-40% gravimetric soil moisture but was lowest in wet soils (greater than 30%). Transformants appeared in soil after 24hr and persisted for up to 15 days even when eDNA concentrations were only a fraction of that found in field soils. Overall, our results show that natural transformation allows eARGs to spread and persist in antibiotic-free soils and that the biological activity of eDNA past bacteria death makes environmental eARGs a public health concern.