Increasing phosphorus ratios between overlying and surface water inhibits intracellular antibiotic resistance gene transformation in a large shallow lake

Abstract

The rising prevalence of antibiotic resistance genes (ARGs) in the surface waters of lakes poses a significant threat to human health. The overlying water in these lakes serves as a critical hotspot for the accumulation of ARGs in surface water. However, the mobility of extracellular (adsorbed ARGs (a-eARGs) and free ARGs (f-eARGs)), and intracellular ARGs (i-ARGs) from overlying water to surface water remains unknown. This study examined the mobility of ARGs between water layers, as well as the underlying mechanisms involved. Significant variations in ARG abundance were observed between overlying and surface water according to PCoA analysis (p < 0.05), with significant reductions in i-ARGs (p < 0.05) in surface water and no significant difference in a-eARGs and f-eARGs. Aminoglycoside and tetracycline i-ARGs had the highest and lowest mobility from overlying water to surface water, respectively. Additionally, the transformation of i-ARGs from overlying water to surface water was significantly correlated with total phosphorus ratio. According to the direct analysis of partial least squares-path modeling, the key drivers of a- and f-eARGs movement from overlying water to surface water were free-living and particle-attached bacteria, respectively, whereas heavy metals gradually became the driving force for i-ARGs by regulating mobile genetic elements. This study illustrated the transmission mechanisms of ARGs from overlying water to surface water in lakes, which will be useful for ARG treatment strategies, especially in eutrophic water.