Adsorptive Interaction Of Extracellular DNA With Biochar And Its Effect On DNA Degradation And Transformation

Extracellular DNA(eDNA)exists outside of the cells,which is widespread in the environment.Extracellular antibiotic resistance genes(eARGs),which use eDNA as a carrier and are transmitted between species through horizontal transfer,pose a threat to human health and have become a new type of internationally recognized pollutant.Biochar is widely used in agriculture and environment as an environmental functional material.Most previous studies have focused on the interaction between eDNA and soil praticles,minerals,nanomaterials,but few have studied the interaction between eDNA and biochars,especially the adsorption,degradation and transformation behavior of eDNA in the presence of biochars.In this paper,the adsorption,desorption,degradation and transformation behaviors of eDNA in biochar system are systematically studied.Following results were obtained by studying the adsorption,desorption,degradation and transformation of eDNA in biochars system:(1)Adsorption kinetics and adsorption isotherms of eDNA on biochars were well fitted by the pseudo-second-order kinetic model and Freundlich isothermal model,respectively.The eDNA adsorption affinity by BCs was ranked as:Wheat straw biochar>Peanut shell biochar>Sawdust biochar.The adsorption of eDNA on biochars has obvious desorption hysteresis phenomenon,and desorption hysteresis factor is close to 1.Increasing the solution ionic strength(10-100 m M Na Cl and 5-25 m M Ca Cl₂)or decreasing p H to less than 5.0significantly increased the adsorption of eDNA on biochars.When p H rises from 5.0 to 10.0,the amount of eDNA adsorption on biochars changed faintly.Electrostatic interaction,Ca ion bridge interaction,?-?interaction were main influence mechanism of adsorption between eDNA and BC,while ligand exchange and hydrophobic interactions were minor contributors.(2)Biochars had a certain protective effect on eDNA,but different biochars had various effects of enzyme degradation.The order of the protective effect of three biochars on eDNA was:Sawdust biochar>Peanut shell biochar>Wheat straw biochar.Adsorbed eDNA can be partially degraded by the nuclease,while adsorbed nuclease almost lost its ability to degrade eDNA.Adsorption of nuclease by biochar was the main mechanism affecting the degradation of eDNA by nuclease.(3)Biochars have an inhibitory effect on transformation of plasmid e ARG,and the inhibition effect of high temperature biochars on transformation activity of plasmid e ARG is stronger than that of low temperature biochars.With the biochars concentration increasing,the inhibition effect of biochars on plasmid e ARG was enhanced.Inhibition of e ARG transformation activity by rice straw biochars was stronger than that of peanut shell biochars.In low temperature biochars system,the main inhibitory effect of biochars on e ARG was from biochar filtrates.In high temperature biochars system,the inhibitory effect of biochars on e ARG was from biochar particle.These findings have important application potential for biochars in eDNA propagation management and environmental fate.