Zhao Gang, Li Enze, Li Jianjun, Liu Fei, Yang Xunan, Xu Meiying
Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Institute of Microbiology, Guangdong Academy of Sciences, Guangzhou, China.
State Key Laboratory of Applied Microbiology Southern China, Guangzhou, China.
Front Microbiol. 2019 Jul 18;10:1623. doi: 10.3389/fmicb.2019.01623. eCollection 2019.
Flavin mononucleotide (FMN) and riboflavin are structurally similar flavins, except for the presence of a phosphate group on the FMN molecule. They are used by a variety of electroactive bacteria as extracellular electron shuttles in microbial Fe reduction and inevitably interact with Fe (hydr)oxides in the extracellular environment. It is currently unknown whether flavin/Fe (hydr)oxide interaction interferes with extracellular electron transfer (EET) to the mineral surface. In this study, we found that the goethite reduction rate was lower when mediated by FMN than by RF, suggesting that FMN was less effective in shuttling electrons between cells and minerals. Nevertheless, the phosphate group did not prevent the FMN molecule from accepting electrons from bacterial cells and transferring electrons to the mineral. Results of adsorption experiment, attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy, and bacterial attachment trend analyses showed that FMN exhibited strong adsorption on goethite surface by forming phosphate inner-sphere complex, which prevented bacterial cells from approaching goethite. Therefore, the interaction between FMN and goethite surface may increase the distance of electron transfer from bacterial cells to goethite and result in lower EET efficiency in comparison to those mediated by riboflavin. To our knowledge, these data reveal for the first time that the interaction between flavin and Fe (hydr)oxide affect flavin-mediated electron transfer to mineral surface and add a new dimension to our understanding of flavin-mediated microbial Fe reduction processes.
黄素单核苷酸（FMN）和核黄素在结构上是相似的黄素，只是FMN分子上存在一个磷酸基团。它们被多种电活性细菌用作微生物铁还原过程中的细胞外电子穿梭体，并且不可避免地会与细胞外环境中的铁（氢）氧化物相互作用。目前尚不清楚黄素/铁（氢）氧化物相互作用是否会干扰向矿物表面的细胞外电子转移（EET）。在本研究中，我们发现由FMN介导时针铁矿的还原速率低于由核黄素介导时，这表明FMN在细胞与矿物之间穿梭电子的效率较低。然而，磷酸基团并没有阻止FMN分子从细菌细胞接受电子并将电子转移到矿物上。吸附实验、衰减全反射（ATR）傅里叶变换红外（FTIR）光谱以及细菌附着趋势分析的结果表明，FMN通过形成磷酸内球络合物在针铁矿表面表现出强烈吸附，这阻止了细菌细胞接近针铁矿。因此，与核黄素介导的情况相比，FMN与针铁矿表面之间的相互作用可能会增加从细菌细胞到针铁矿的电子转移距离，并导致EET效率降低。据我们所知，这些数据首次揭示了黄素与铁（氢）氧化物之间的相互作用会影响黄素介导的向矿物表面的电子转移，并为我们对黄素介导的微生物铁还原过程的理解增添了新的维度。
