How microorganisms respond to single and binary antibiotic exposure: Focusing on detoxification, nitrogen, phosphorus, and cell metabolism mechanisms

The coexistence of multiple antibiotics poses a significant threat to biological treatment systems. However, few studies have systematically explored their comprehensive impact on the metabolic performance of microorganisms. This study examined the effects of sulfadiazine (SDZ) and norfloxacin (NOR) on microbial enzyme activity, electron transport system, oxidative stress, detoxification, and metabolic capabilities after long-term exposure to environmental concentrations (0.01–0.5 mg/L). Our results demonstrated that single and coexposure to SDZ and NOR significantly enhanced the activities of ammonia monooxygenase and hydroxylamine oxidase, induced oxidative damage, and inhibited electron transfer and nitrate reductase activity. Metatranscriptomics analysis revealed that SDZ and NOR, either alone or in combination, shortcut nitrification and denitrification, replacing the traditional nitrification-denitrification pathway as the dominant nitrogen removal pathway. Compared to single exposure, microorganisms under coexposure conditions exhibited enhanced detoxification capacity by upregulating genes associated with toxic efflux and carbon metabolism and promoting polyphosphate accumulation and transformation. Coexposure particularly worsens the ability of cell mobility but can mainly improve toxicity resistance between microorganisms by enhancing putrescine and glutamate transport. This research enhances our understanding of the impact of multi-pollutant interactions on wastewater treatment performance and biological metabolic mechanisms.