Supported by the National Science Fund for Excellent Young Scholars of China (No. 42222703)
土壤胞外呼吸是驱动元素生物地球化学循环的引擎，而微生物纳米导线是实现土壤胞外呼吸的重要途径。微生物纳米导线是一类生长于微生物表面，可长达数十微米的具有导电性的纤维状结构。它直接作用于微生物与土壤矿物、产甲烷与甲烷氧化微生物间的电子传递，从而影响了土壤矿物的迁移转化及温室气体减排。Geobacter sulfurreducens是研究微生物纳米导线的模式微生物。长久以来，基于分子生物学实验证据表明，G. sulfurreducens纳米导线是PilA-N菌毛。而最近基于冷冻电镜技术的纳米导线结构分析发现，G. sulfurreducens实际上表达着各种形式的细胞色素c纳米导线。自此，关于“纳米导线本质”的问题成为学术界争论的焦点。以G. sulfurreducens纳米导线理论发展为主线，综述了不同时期对纳米导线结构与功能的认识，并系统分析了作为“纳米导线本质”争议的证据基础，将推动该争议的早日解决，并助力土壤胞外呼吸理论的成熟及微生物纳米导线的应用研究。
Soil extracellular respiration is the engine driving the global biogeochemical cycle, in which microbial nanowires serve as an important pathway for microbes to realize it. Microbial nanowires are electrically conductive fibrous structures that can be tens of microns long and grow on the surface of microorganisms. It directly works on the electron transfer between microorganisms and soil minerals, biomethanation and methanogens, etc, thus affecting the migration and transformation of soil minerals and the emission reduction of greenhouse gases. Microbial nanowires were originally discovered on the surface of Geobacter sulfurreducens when the strain was reducing ferrihydrite. G. sulfurreducens is widely distributed in paddy fields, wetlands, reducing soil, and surface sediments. Due to the abundant extracellular nanowires, G. sulfurreducens occupies a key niche in the food chain of anaerobic microorganisms and participates in the global biogeochemical cycling of some key elements, such as C, N, S and Fe. Because of the accessibility to complete genomic information and genetic maneuverability, G. sulfurreducens has become the model microorganism for studying microbial nanowires. For a long time, experimental evidence based on molecular biology has shown that G. sulfurreducens nanowires are conductive type IV PilA-N pili composed of PilA monomeric subunits and multiple conceived models of electron transfer in PilA-N pili have been developed. However, the recent nanowire structure analysis based on cryo-electron microscopy(cryo-EM) found that G. sulfurreducens expressed various c-type cytochrome nanowires, including but may not be limited to OmcS nanowire, OmcZ nanowire and OmcE nanowire, which were anatomically different conductive cytochrome nanowires with their specific electron transfer roles in G. sulfurreducens. Furthermore, the cryo-EM also showed the expression of PilA-N-C pili, which was located in periplasm, hardly had electronic conductivity, and mainly functioned at assisting the secretion of cytochrome nanowires. The lack of either conductivity or typical type IV nanowire functions indicated that the biological role of PilA-N-C pili is completely different from the previously described PilA-N pili of G. sulfurreducens but is pseudo-pili-like. All these findings constantly questioned and challenged the theory of PilA-N pili. Since then, the issue of "the nature of nanowires" has become the focus of academic debate. As the saying goes, "the more the truth is debated, the clearer it will be." Here, the timeline of G. sulfurreducens nanowires' theoretic studies is taken to summarize the understanding of the structure and function of nanowires. Also, the evidence based on the "nature of nanowires" dispute is systematically analyzed, which will promote the early settlement of the dispute, as well as help mature the theory of soil extracellular respiration and the application of microbial nanowires.
叶银,周顺桂,刘星.微生物纳米导线的结构与功能：争议及进展[J].土壤学报,2024,61(2):297-307. DOI:10.11766/trxb202303140103 YE Yin, ZHOU Shungui, LIU Xing. Structure and Function of Microbial Nanowires: Controversy and Progress[J]. Acta Pedologica Sinica,2024,61(2):297-307.复制