Effects of particle size and pyrolytic temperature of biochar on the transformation behavior of antibiotic resistance genes

Abstract

Rampant use of antibiotics has caused a rapid dissemination of antibiotic resistance genes (ARGs) in environment, posing great threats to ecosystems and human health. Applying biochar (BC) in natural systems to combat the spread of ARGs arises as an attention-grabbing solution. Unfortunately, the effectiveness of BC is still unmanageable due to the incomprehensive knowledge over correlations between BC properties and extracellular ARGs transformation. To pinpoint the crucial factors, we primarily explored transformation behaviors of plasmid-mediated ARGs exposed to BC (in suspensions or extraction solutions), adsorption capacities of ARGs on BC, and growth inhibition of E. coli imposed by BC. Specifically, the effects of BC properties including particle size (large-particulate 150 μm and colloidal 0.45–2 μm) and pyrolytic temperature (300, 400, 500, 600, and 700 °C) on the ARGs transformation were emphasized. Results showed that both large-particulate BC and colloidal BC, irrespective of their pyrolytic temperature, would induce significant inhibitory effects on the ARGs transformation, while the BC extraction solutions showed little effect except BC pyrolyzed at 300 °C. Correlation analysis uncovered that the inhibition effect of BC on ARGs transformation was tightly correlated with its adsorption capacity towards plasmid. Accordingly, greater inhibitory effects from those BCs with higher pyrolytic temperatures and smaller particle sizes mainly originated from their greater adsorption capacities. Intriguingly, E. coli was unable to ingest the plasmid adsorbed on BC, which led to ARGs blocked outside the cell membrane, although this inhibitory effect was partially affected by survival inhibition of BC on E. coli. Particularly, significant plasmid aggregation could occur in the extraction solution of large-particulate BC pyrolyzed at 300 °C, leading to a significant inhibition of ARGs transformation. Overall, our findings complete the insufficient understanding over the effects of BC on ARGs transformation behavior, and potentially provide new insights to scientific communities in mitigating ARGs spreading.