State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, 712100, China; University of Chinese Academy of Sciences, Beijing, 100049, China; College of Xingzhi, Zhejiang Normal University, Jinhua, 321000, China.
State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, 712100, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
Environ Pollut. 2019 Jul;250:118-126. doi: 10.1016/j.envpol.2019.03.123. Epub 2019 Apr 9.
Metal-resistant bacteria can survive exposure to high metal concentrations without any negative impact on their growth. Biosorption is considered to be one of the more effective detoxification mechanisms acting in most bacteria. However, molecular-scale characterization of metal biosorption by wild metal-resistant bacteria has been limited. In this study, the Pb(II) biosorption behavior of Serratia Se1998 isolated from Pb-contaminated soil was investigated through macroscopic and microscopic techniques. A four discrete site non-electrostatic model fit the potentiometric titration data best, suggesting a distribution of phosphodiester, carboxyl, phosphoryl, and amino or hydroxyl groups on the cell surface. The presence of these functional groups was verified by the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, which also indicated that carboxyl and phosphoryl sites participated in Pb(II) binding simultaneously. The negative enthalpy (-9.11 kJ mol) and large positive entropy (81.52 J mol K) of Pb(II) binding with the bacteria suggested the formation of inner-sphere complexes by an exothermic process. X-ray absorption fine structure (XAFS) analysis further indicated monodentate inner-sphere binding of Pb(II) through formation of C-O-Pb and P-O-Pb bonds. We inferred that C-O-Pb bonds formed on the flagellar surfaces, establishing a self-protective barrier against exterior metal stressors. This study has important implications for an improved understanding of metal-resistance mechanisms in wild bacteria and provides guidance for the construction of genetically engineered bacteria for remediation purposes.
耐金属细菌可以在不受任何生长负面影响的情况下暴露于高浓度金属中。生物吸附被认为是大多数细菌中更有效的解毒机制之一。然而，野生耐金属细菌的金属生物吸附的分子尺度表征一直受到限制。在这项研究中，通过宏观和微观技术研究了从 Pb 污染土壤中分离出的 Serratia Se1998 对 Pb(II)的生物吸附行为。一个四离散位点非静电模型最适合电位滴定数据，表明细胞表面存在磷酸二酯、羧基、磷酸基和氨基或羟基基团的分布。衰减全反射傅里叶变换红外光谱（ATR-FTIR）证实了这些官能团的存在，ATR-FTIR 还表明羧基和磷酸基位点同时参与了 Pb(II)的结合。Pb(II)与细菌结合的负焓（-9.11 kJ/mol）和大的正熵（81.52 J/mol K）表明形成了内球络合物，这是一个放热过程。X 射线吸收精细结构（XAFS）分析进一步表明，Pb(II)通过形成 C-O-Pb 和 P-O-Pb 键以单齿内球结合。我们推断 C-O-Pb 键在鞭毛表面形成，建立了一个自我保护屏障，防止外部金属胁迫剂的侵害。这项研究对深入了解野生细菌的金属抗性机制具有重要意义，并为构建用于修复目的的基因工程细菌提供了指导。
