Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry Universitygrid.256111.0, Fuzhou, China.
Department of Earth Science, University of Southern Californiagrid.42505.36, Los Angeles, California, USA, United States.
mBio. 2021 Feb 22;13(1):e0382221. doi: 10.1128/mbio.03822-21. Epub 2022 Feb 15.
Conductive nanowires are thought to contribute to long-range electron transfer (LET) in Geobacter sulfurreducens anode biofilms. Three types of nanowires have been identified: pili, OmcS, and OmcZ. Previous studies highlighted their conductive function in anode biofilms, yet a structural function also has to be considered. We present here a comprehensive analysis of the function of nanowires in LET by inhibiting the expression of each nanowire. Meanwhile, flagella with poor conductivity were expressed to recover the structural function but not the conductive function of nanowires in the corresponding nanowire mutant strain. The results demonstrated that pili played a structural but not a conductive function in supporting biofilm formation. In contrast, the OmcS nanowire played a conductive but not a structural function in facilitating electron transfer in the biofilm. The OmcZ nanowire played both a structural and a conductive function to contribute to current generation. Expression of the poorly conductive flagellum was shown to enhance biofilm formation, subsequently increasing current generation. These data support a model in which multiheme cytochromes facilitate long-distance electron transfer in G. sulfurreducens biofilms. Our findings also suggest that the formation of a thicker biofilm, which contributed to a higher current generation by G. sulfurreducens, was confined by the biofilm formation deficiency, and this has applications in microbial electrochemical systems. The low power generation of microbial fuel cells limits their utility. Many factors can affect power generation, including inefficient electron transfer in the anode biofilm. Thus, understanding the mechanism(s) of electron transfer provides a pathway for increasing the power density of microbial fuel cells. Geobacter sulfurreducens was shown to form a thick biofilm on the anode. Cells far away from the anode reduce the anode through long-range electron transfer. Based on their conductive properties, three types of nanowires have been hypothesized to directly facilitate long-range electron transfer: pili, OmcS, and OmcZ nanowires. However, their structural contributions to electron transfer in anode biofilm have not been elucidated. Based on studies of mutants lacking one or more of these facilitators, our results support a cytochrome-mediated electron transfer process in biofilms and highlight the structural contribution of nanowires in anode biofilm formation, which contributes to biofilm formation and current generation, thereby providing a strategy to increase current generation.
导电纳米线被认为有助于 Geobacter sulfurreducens 阳极生物膜中的长程电子转移 (LET)。已经鉴定出三种纳米线：菌毛、OmcS 和 OmcZ。先前的研究强调了它们在阳极生物膜中的导电功能，但也必须考虑其结构功能。我们在这里通过抑制每种纳米线的表达，对纳米线在 LET 中的功能进行了全面分析。同时，表达了导电性差的鞭毛以恢复相应纳米线突变菌株中纳米线的结构功能，但不恢复其导电功能。结果表明，菌毛在支持生物膜形成中起结构作用而不起导电作用。相比之下，OmcS 纳米线在促进生物膜中的电子传递中起导电作用而不起结构作用。OmcZ 纳米线起结构和导电作用以促进电流产生。表达导电性差的鞭毛被证明可以增强生物膜的形成，从而增加电流的产生。这些数据支持了这样一种模型，即多血红素细胞色素促进了 G. sulfurreducens 生物膜中的长程电子转移。我们的发现还表明，由 G. sulfurreducens 形成的更厚的生物膜会限制电流的产生，因为生物膜形成不足，这在微生物电化学系统中有应用。微生物燃料电池的低发电功率限制了它们的实用性。许多因素会影响发电，包括阳极生物膜中电子转移效率低下。因此，了解电子转移的机制为提高微生物燃料电池的功率密度提供了途径。已经表明 Geobacter sulfurreducens 在阳极上形成厚的生物膜。远离阳极的细胞通过长程电子转移还原阳极。基于它们的导电特性，已经假设三种类型的纳米线直接促进长程电子转移：菌毛、OmcS 和 OmcZ 纳米线。然而，它们在阳极生物膜中电子转移的结构贡献尚未阐明。基于缺乏一种或多种这些促进剂的突变体的研究，我们的结果支持了生物膜中细胞色素介导的电子转移过程，并强调了纳米线在阳极生物膜形成中的结构贡献，这有助于生物膜的形成和电流的产生，从而提供了一种增加电流产生的策略。
