微生物纳米导线的结构与功能:争议及进展OA北大核心CSTPCD

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.