Responses of soil antibiotic resistance genes to the decrease in grain size of sediment discharged into Dongting Lake, China.

Sediment or soil in wetlands is regarded as an important sink of antibiotic resistance genes (ARGs). However, there are no studies on the effects of sediment changes (which caused changes in soil texture) on soil ARGs in wetland. Here, we collected topsoil samples from 12 study sites that were deposited in early (prior to the 1970s) or recent years to reveal the responses of soil ARGs to the decrease in grain size of sediment discharged into Dongting Lake. The results indicated that it caused significant increases in clay content, soil organic matter (SOM), moisture, and bacterial abundance. The absolute abundance of 38 % ARG subtypes, 62 % ARG types, and the total ARG concentrations showed a significant increase. The composition of ARG profiles also showed significant changes. For mobile genetic elements (MGEs), the levels of plasmid, insertional, and transposase were significantly elevated. Notably, clay content, moisture, SOM, and bacterial abundance presented very strong positive correlation with most ARG and total ARG abundance. The contributions of physicochemical characteristics and bacterial abundance to ARG variations were ranked as follows: 16S rRNA > SOM > moisture > pH > soil texture (clay, sand and silt) > nitrate nitrogen > ammonium nitrogen. Bacterial abundance, SOM, moisture, and soil texture were the primary environmental parameters contributing to the soil ARG variations in this research. These changes of ARGs may pose risks to ecosystems and public health.