Effect Of Ion Type On The Co-migration Of Resistant Plasmids And Kaolin Colloidal Particles In Saturated Porous Media

Resistance genes are a kind of Emerging contaminants that is closely related to the abuse of antibiotics.Since the resistance gene has biological properties that can be expressed and amplified by microorganisms and propagated between microorganisms,the environmental health risks are even more serious than the simple antibiotic contamination.The plasmid carrying the resistance gene can exist in a free state in an aqueous environment,and enters other microorganisms through transformation,so that other microorganisms develop resistance.As a colloidal type widely existed in groundwater environment and soil environment,clay colloid has certain carrying and protective effects on antagonistic plasmids,and is an important factor affecting the spread of drug resistance genes in microorganisms in the environment.Studying the transportation effect of clay colloid on the resistance plasmid is very necessary for predicting the concentration distribution and evolution trend of drug-resistant bacteria in environmental media.Groundwater environments contain a variety of ions.Currently,the effects of different ions on the co-transportation of clay colloids,resistant plasmids,and clay colloid-resistant plasmids are unclear.In order to study the transportation of clay colloids and resistant plasmids in environmental media,the transportation process of the two was simulated by continuous flow column experiments.The study used iron oxide quartz sand to fill a 3 cm flow column to simulate porous media.At the same time,the kaolin colloid was used to represent the clay colloid widely present in the environment.The typical resistant plasmid pBR322 was used to represent the resistant plasmid in the environment.The three salt solutions(the NaCl solution,Na₂SO₄ solution and NaNO₃ solution were used to simulate Cl^-,SO₄^2-,NO₃^- and Na⁺ in the eight major ion species in the groundwater environment.The concentration of the kaolin colloid and pBR322 plasmid before entering the iron oxide quartz sand column reflected the change in sand.transportation in the column.The transportation and co-transportation of pBR322 plasmid and kaolin colloid in three salt solutions?NaCl,Na2SO4,NaNO3?and two ionic strengths?30 mM and 300 mM? were investigated.The results show that the transportation ability of kaolin colloid in different salt solutions is Na₂SO₄>NaNO₃>NaCl from strong to weak.The transportation ability of the pBR322 plasmid was also different at different ionic strengths,and its transportation ability at 300 mM ionic strength was higher than that at 30 mM ionic strength.Moreover,after co-transportation experiments of pBR322 plasmid and kaolin colloid,it was found that pBR322 plasmid inhibited the transportation of kaolin colloid,and kaolin colloid promoted the transportation of pBR322 plasmid.These findings imply that the presence of clay colloids in the groundwater environment not only hinders the degradation of resistant plasmids in the environment,but also enhances their transportation and transmission effects,thereby increasing the risk of resistance genes spreading in groundwater environments.