Doxycycline combined manure microbes to enhances biofilm formation of the soil plastisphere and increases the surface bio-risk of microplastics vehicle

Microbial biofilms can protect bacteria against environmental stresses, such as antibiotics. Microplastics (MPs) provide attachment sites for microbes to form biofilms in aquatic systems; however, in terrestrial systems, research is still lacking, especially in croplands under fertilization and antibiotic exposure. The present study revealed the effects of different doxycycline (DOX) concentrations on the soil plastisphere by examining biofilm formation regularity and the risk posed by MP-attached strains during manuring. The results showed that soil MP biofilm formation could be enhanced by DOX exposure, especially in low-DOX-concentration group over 60 days, and the biofilm formation gene (BFG) expression level on MPs was stronger in low-DOX-exposure group. DOX exposure increased the abundance of most tet genes on the MPs, and the intl1 abundance was highly increased in the DOX exposure groups (enhanced to 1.07 × 108–8.37 × 107 copies/g). DOX exposure increased the diversity of bacteria that were both potential antibiotic resistance gene (ARG) hosts and biofilm-producing strains on MPs, and low DOX exposure enhanced the abundance of potential pathogens on MPs. The correlations among biofilms, ARGs and DOX on soil MPs were promoted by DOX exposure. Further experiments also proved that both MPs and DOX existing enhanced the biofilm production ability of the strains, and the biofilm production ability of the strains attached to the MPs was stronger than that of planktonic cells. This study revealed that DOX exposure, typically low concentrations of DOX, could increase ARG transfer and the abundance of residual pathogens on MPs through biofilm production and the associated protection during manuring.