Molecular Insight into the Binding Property and Mechanism of Sulfamethoxazole to Extracellular Proteins of Anammox Sludge

Abstract

Antibiotics are widely found in nitrogen-containing wastewater, which may affect the operation stability of anaerobic ammonium oxidation (anammox)-based biological treatment systems. Extracellular polymeric substances (EPSs) of anammox sludge play a pivotal role in combining with antibiotics; however, the exact role and how the structure of the leading component of EPSs (i.e., extracellular proteins) changes under antibiotic stress remain to be elucidated. Here, the interaction between sulfamethoxazole and the extracellular proteins of anammox sludge was investigated via multiple spectra and molecular simulation. Results showed that sulfamethoxazole statically quenched the fluorescent components of EPSs, and the quenching constant of the aromatic proteins was the largest, with a value of 1.73 × 104 M–1. The overall binding was an enthalpy-driven process, with ΔH = −75.15 kJ mol–1, ΔS = −0.175 kJ mol–1 K–1, and ΔG = −21.10 kJ mol–1 at 35 °C. The O-P-O and CO groups responded first under the disturbance of sulfamethoxazole. Excessive sulfamethoxazole (20 mg L–1) would decrease the ratio of α-helix/(β-sheet + random coil) of extracellular proteins, resulting in a loose structure. Molecular docking and dynamic simulation revealed that extracellular proteins would provide abundant sites to bind with sulfamethoxazole, through hydrogen bond and Pi-Akyl hydrophobic interaction forces. Once sulfamethoxazole penetrates into the cell surface and combines with the transmembrane ammonium transport domain, it may inhibit the NH4 + transport. Our findings enhance the understanding on the interaction of extracellular proteins and sulfamethoxazole, which may be valuable for deciphering the response property of anammox sludge under the antibiotic stress.

Adding exogenous protein relieves the toxicity of nanoparticles to anammox granular sludge by adsorption and the formation of eco-coronas

“…50 According to Lotti et al , 51 the content of proteins in the anammox EPS is more than 60%. Li et al 52 discovered more than 1600 types of proteins in it, dominated by the peptide ABC transporter substrate-binding protein, molybdopterin-dependent oxidoreductase and alginate export family protein. During the penetration of MgO NPs through the EPS layer, they inevitably interacted with the proteins in EPS of anammox granular sludge.…”

Extracellular polymeric substances—antibiotics interaction in activated sludge: A review

“…c , The order priority of sludge EPS components interacted with tetracycline, modified from Ref. [ 1 ]; copyright (2021) Elsevier. …”

“…Specifically, a noteworthy observation of higher EPS production and a higher portion of α-helice was found for aerobic sludge EPS than for the anaerobic sludge systems [ 44 , 82 , 85 ]. Compared with the floc sludge, higher contents of proteins with larger molecular weights (such as aromatic and tryptophan proteins) detected in the granular sludge than those in flocs sludge might be the reason that the granular sludge exhibits superior resistance to antibiotics [ 1 , 86 ]. Additionally, higher contents were preferentially observed in granular sludge than floc sludge, which might be the main reason for its excellent resistance to the toxic stress of antibiotics [ 58 , 87 ].…”

“…Antibiotics are the most frequently used pharmaceuticals for preventing and treating infectious diseases in humans and animals, with global consumption of 42 billion defined daily doses in recent years [ 1 ]. Since the antibiotics used are only partially metabolized in the human and animal digestive tracts, large amounts of antibiotics are discharged into the aquatic ecosystem from point sources (pharmaceutical industries, hospitals, and households) and nonpoint sources (agricultural and urban runoffs) [ 2 ], leading to severe pollution throughout the world.…”

“…In addition to being an extracellular physical barrier, EPS could also provide many functional groups (e.g., carboxyl, hydroxyl, amino, phosphoryl, and sulfhydryl groups) for contaminant adhesion and further decrease their exposure risk and toxic stress [ 8 ]. Undoubtedly, EPS play a dominant role in antibiotics adsorption, preventing their direct contact with microbes to endow microbes with resistance to antibiotics [ 1 ].…”