Surfactant aggravated the antibiotic's stress on antibiotic resistance genes proliferation by altering antibiotic solubilization and microbial traits in sludge anaerobic fermentation

The excessive application of antibiotics and surfactants resulted in their massive accumulation in waste activated sludge (WAS), but the co-occurrent impacts of antibiotics and surfactants on the antibiotic resistant genes (ARGs) fates have seldom reported. This work mainly revealed the roles and critical mechanisms of sodium dodecyl benzene sulfonate (SDBS) on the sulfadiazine (SDZ) stressing for ARGs distribution during WAS anaerobic fermentation. High-throughput qPCR and metagenomic analysis revealed that SDBS aggravated the SDZ selective pressure, and accelerated the proliferation of ARGs. The total abundance of ARGs was increased from 8.81 × 10¹⁰ in SDZ to 1.17 × 10¹¹ copies/g TSS in the SDBS/SDZ co-occurrence system. Specifically, the absolute abundances of ermF (MLSB), mefA (MLSB), tetM-01 (tetracycline), tetX (tetracycline), sul2 (sulfonamide) and strB (aminoglycoside) were risen from 4.60 × 10⁸–7.44 × 10⁹ copies/g TSS in the SDZ reactor to 1.02 × 10⁹–4.63 × 10¹⁰ copies/g TSS in SDBS/SDZ reactor. SDBS was contributed to the SDZ solubilization and simultaneously effective in disintegrating extracellular polymeric substances and improving cell membrane permeability, which would facilitate the SDZ transport and its interactions with ARGs hosts. Consequently, the microbial community structure was evidently altered, and the typical ARGs hosts (i.e., Saccharimonadales and Ahniella) were greatly enriched. Also, the cell signal transduction systems (i.e., glnL, glrK and pilG), oxidative stress response (i.e., frmA and recA) and bacterial secretion systems (i.e., VirB4), which were related with ARGs propagation, were all provoked in the co-occurred SDBS/SDZ reactor compared with that of sole SDZ. PLS-PM analysis suggested that the bacterial community was the predominant factor that determined the ARGs fates, followed by mobile genetic elements and metabolic pathway. This work demonstrated the interactive effects of surfactants and antibiotics on the ARGs fates in WAS fermentation systems and gave insightful implications on the ecological risks of different exogenous pollutants.