The effect of sulfamethoxazole on methanogenesis and intracellular and extracellular antibiotic resistant genes transmission in anaerobic granular sludge

Anaerobic granular sludge has been extensively utilized in anaerobic wastewater treatment due to its stable structure and strong resistance to shock loads. However, the mechanisms by which varying concentrations of sulfamethoxazole (SMX) influence methane production, as well as the transmission of intracellular and extracellular antibiotic resistance genes (ARGs), remain unclear. This study investigated the effects of SMX concentration on methane production and intracellular and extracellular ARGs transfer behavior during anaerobic wastewater treatment. Results showed that the final methane yield was 333.2, 470.1, 199.1, and 7.2 mL/gCOD, respectively, under 0, 0.5, 5, and 10 mg/L SMX. 0.5 mg/L SMX enhanced methane yield by 41.1 %. This enhancement was attributed to the stimulation of extracellular polymeric substances and catalase secretion, which alleviated oxidative stress caused by reactive oxygen species and increased the abundance of Methanosaeta and Methanobacterium. Simultaneously, the spread of both intracellular and extracellular ARGs was suppressed through the regulation of host microbial communities, specifically reflected in the reduced abundance of ARGs, decreased abundance of cell membrane permeability genes and the type IV secretion system. In contrast, 5 and 10 mg/L SMX inhibited methane production while facilitating ARGs dissemination. This study demonstrated that SMX concentrations significantly affected methane production and the prevalence of ARGs during anaerobic wastewater treatment.