School of Environment and Safety Engineering, North University of China, Taiyuan 030051, China; Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, School of Environment and Energy, South China University of Technology, Guangzhou 510006, China.
Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, School of Environment and Energy, South China University of Technology, Guangzhou 510006, China.
J Hazard Mater. 2023 Aug 5;455:131544. doi: 10.1016/j.jhazmat.2023.131544. Epub 2023 May 6.
Extracellular biodegradation is a promising technology for removing antibiotics and repressing the spread of resistance genes, but the strategy is limited by the low extracellular electron transfer (EET) efficiency of microorganisms. In this work, biogenic Pd nanoparticles (bio-Pd) were introduced in cells in situ to enhance oxytetracycline (OTC) extracellular degradation and the effects of transmembrane proton gradient (TPG) on EET and energy metabolism mediated by bio-Pd were investigated. The results indicated that the intracellular OTC concentration gradually decreased with increase in pH due to the simultaneous decreases of OTC adsorption and TPG-dependent OTC uptake. On the contrary, the efficiency of OTC biodegradation mediated by bio-Pd@B. megaterium showed a pH-dependent increase. The negligible intracellular OTC degradation, the high dependence of OTC biodegradation on respiration chain and the results on enzyme activity and respiratory chain inhibition experiments showed that NADH-dependent (rather than FADH-dependent) EET process mediated by substrate-level phosphorylation modulated OTC biodegradation due to high energy storage and proton translocation capacity. Moreover, the results showed that altering TPG is an efficient approach to improve EET efficiency, which can be attributed to the increased NADH generation by the TCA cycle, enhanced transmembrane electron output efficiency (as evidenced by increased intracellular electron transfer system (IETS) activity, the negative shift of onset potential, and enhanced one-electron transfer through bound flavin) and stimulation of substrate-level phosphorylation energy metabolism catalyzed by succinic thiokinase (STH) under low TPG conditions. The results of structural equation model that OTC biodegradation was directly and positively modulated by the net outward proton flux as well as STH activity, and indirectly regulated by TPG through NADH level and IETS activity confirmed the previous findings. This study provides a new perspective for engineering microbial EET and application of bioelectrochemistry processes in bioremediation.
胞外生物降解是去除抗生素和抑制抗性基因传播的一种很有前途的技术，但该策略受到微生物胞外电子转移 (EET) 效率低的限制。在这项工作中，将生物合成的 Pd 纳米颗粒 (bio-Pd) 引入细胞内原位，以增强土霉素 (OTC) 的胞外降解，研究了跨膜质子梯度 (TPG) 对 bio-Pd 介导的 EET 和能量代谢的影响。结果表明，由于 OTC 吸附和 TPG 依赖的 OTC 摄取同时减少，随着 pH 值的增加，细胞内 OTC 浓度逐渐降低。相反，生物-Pd@B. megaterium 介导的 OTC 生物降解效率表现出 pH 依赖性增加。微不足道的细胞内 OTC 降解、OTC 生物降解对呼吸链的高度依赖以及酶活性和呼吸链抑制实验的结果表明，由于具有较高的储能和质子迁移能力，依赖 NADH（而不是依赖 FADH）的 EET 过程（通过底物水平磷酸化介导）调节 OTC 生物降解。此外，结果表明，改变 TPG 是提高 EET 效率的有效方法，这可归因于 TCA 循环增加了 NADH 的产生、增强了跨膜电子输出效率（表现为细胞内电子转移系统 (IETS) 活性增加、起始电位负移以及通过结合黄素增强了单电子转移）以及在低 TPG 条件下促进琥珀酸硫激酶 (STH) 催化的底物水平磷酸化能量代谢。OTC 生物降解直接且正向受净外向质子通量以及 STH 活性调制，间接受 TPG 通过 NADH 水平和 IETS 活性调制的结构方程模型的结果证实了上述发现。这项研究为工程微生物 EET 以及生物电化学过程在生物修复中的应用提供了新视角。
