Impacts of biochars on bacterial community shifts and biodegradation of antibiotics in an agricultural soil during short-term incubation.

This study investigated the effects of applying different biochars to soil on shifts in the bacterial community, the biodegradation of antibiotics, and their relationships. In total, nine biochars were applied to agricultural soil contaminated with 16 antibiotics. Clustering analysis showed that the responses of bacteria at the genus level to biochars were highly dependent on the biochar feedstock rather than the pyrolysis temperature. Among the antibiotics tested in the study, the biodegradation percentage was lower for tetracyclines (TCs, 6-14%) than sulfonamides (SAs, 8-26%) and quinolones (QLs, 8-24%). For specific individual antibiotics from the same class with similar structures, the high adsorption affinity of soil particles for antibiotics due to hydrophobic interactions (logKow) and electrostatic interactions (pKa) resulted in low biodegradation percentages for antibiotics in the soil. The biodegradation of TCs was affected more by the biochar type (effect size: -10% to 42%) than those of QLs (-26% to 14%) and SAs (-24% to 22%). According to the relationships determined between the bacterial taxonomic composition and biodegradation of antibiotics, Steroidobacter from the phylum Proteobacteria has significant positive correlations with the biodegradation of all SAs (p < 0.01), thereby indicating that Steroidobacter had a high capacity for biodegrading SAs. Significant positive correlations were also detected (p < 0.05) between specific genera (Iamia, Parviterribacter, and Gaiella) from the phylum Actinobacteria and the biodegradation of SAs. No significant positive correlations were found between bacterial genera and the biodegradation percentages for QLs and TCs, possibly due to the specific microorganisms involved in these biodegradation processes. The results in this study provide insights into the biodegradation mechanisms of antibiotics in soil and they may facilitate the development of strategies for the bioremediation of antibiotic-contaminated soil.