Promoted sulfamethoxazole extracellular biodegradation in Citrobacter freundii JH@Pd by launching AcrB efflux pump

Abstract

This study found that bio-Pd⁰ nanoparticles could launch proton motive force (PMF)-mediated antibiotics efflux pump (AEP) to confer the detoxification capability on Citrobacter freundii, as evidenced by the highest sulfamethoxazole (SMX) specific degradation rate (81.7 μg L⁻¹ mg⁻¹ protein d⁻¹) at high PMF (pH 6). The batch experiment and RT-qPCR results indicated that bio-Pd⁰ activated the AcrB efflux pump through upregulating the AEP transcriptional regulation factor ramA (2.7–3.1 times), which benefited the intra/extracellular respiration and ATP production/utilization. Path analysis revealed that the prosperity of metabolic activity and extracellular electron output capacity enabled SMX biodegradation, mainly through the electron redistribution and energy optimization with the formate dehydrogenase/hydrogenase based Short-chain (FDH/Hase-S-chain). The upregulation of hypE (2.7–8.6 times) and atpD (1.9–2.3 times) genes encoding the Hase respiratory chain and the F-type ATP synthase, respectively, further supports this mechanism. These novel findings provided a new strategy to improve the biodegradation efficiency of antibiotics wastewater.