Distribution and dynamics of antibiotic resistance genes in sludge under discharge plasma oxidation

Abstract

Antibiotic resistance genes (ARGs), emerging environmental contaminants, have been largely accumulated in sludge during wastewater treatment. Discharge plasma oxidation, an advanced oxidation technology, has been demonstrated as an effective strategy in sludge pretreatment. However, the effect of plasma oxidation on the distribution and dynamics of ARGs in sludge is unknown. Herein, the variations of four typical ARGs (tetC, tetW, blaTEM-1, aac(3)-Ⅱ) and one integron (intI-1) in sludge during discharge plasma treatment were investigated. The results showed that under low discharge voltage or short treatment time, weak plasma oxidation enriched the contents of ARGs and intI-1 in sludge (with 1.14 log unit maximum increment) via proliferating biomass or promoting horizontal gene transfer. Further increasing discharge voltage or prolonging treatment time, strong plasma oxidation eliminated target genes due to the destroyed bacteria or inhibited horizontal transfer of ARGs. Especially, the homogeneous condition greatly promoted the reduction of ARGs in liquid phase (up to 1.52 log unit reduction). Furthermore, the correlation analysis between intI-1 and ARGs implied that tetC and tetW abundances might be significantly affected by intI-1 through horizontal transfer. At the same time, the microbial communities in sludge were investigated to help understand the effect of plasma oxidation on ARGs variation. Notably, the most predominant phylum Proteobacteria and genus Acinetobacter resisted the oxidative infringement from plasma to maintain high relative abundances (52.05 % in solid phase and 84.10 % in liquid phase for Proteobacteria, 13.82 % in solid phase and 78.00 % in liquid phase for Acinetobacter at 20 kV). Meanwhile, the co-occurrence analysis between genes and dominant genera further showed that Romboutsia sp. might be a potential host bacteria of ARGs and intI-1 in solid phase, and Acidovorax sp., Parachlamydia sp., and Armatimonadetes_gp5 sp. might be the potential hosts of tetW, tetC, and intI-1 in liquid phase.