Study On The Selection Of Intracellular Transfer Pathway And The Evaluation Of Extracellular Electron Release In Electricigens

With the wide application in the field of environmental remediation,nanomaterial synthesis and the biological energy in recent years,electricigens have attracted more and more attentions.Shewanella,a typical electricigens,possesses the special extracellular respiratory ability which contributes to the environment adaptability.But the choice of electron transfer pathways in transmembrane electron transfer?TET?of Shewanella is still poorly understood up to date.In particular,the role of CymA,a key cytoplasmic membrane anchored tetrahaem c-type cytochrome in periplasm,in TET is still under debate.In addition,extracellular electron release ability of electricigens has an important influence on its practical application,However,the existing methods have many defects.Thus,development of a convenient,efficient and cheap methods for evaluating the exoelectrogenic ability of electricigens is highly desirable.In this study,Shewanella oneidensis MR-1 has been carried out to investigate the influence of extracellular electron release process on the choice of electron transfer pathways in TET.Furthermore,a novel high-throughput photometric assay based on the extracellular dye reduction was developed to evaluate microbial exoelectrogenic ability.The main conclusions are as follows:?1?Extracellular electron release process affects the choice of intracellular electron transfer way.The character of extracellular electron acceptors determine the importance of c-type cytochrome CymA in TET of Shewanella.CymA played a essential role for ferric citrate reduction,which is an easily-accessible electron acceptor,but for the insoluble Fe₂O₃ reduction,its function is negligible.Accelerating the extracellular electron release by adding riboflavin as an electron mediator,increasing the ferric citrate concentration,or applying a electrode with a higher potential,could significantly enhance the importantce of CymA in TET.Thus,at a high-rate electron transfer process,the dependency of CymA in TET would become prominent.On the contrary,at a slow-rate electron transfer process,some other c-type cytochromes would replace the role of CymA in TET.?2?Microbial exoelectrogenic ability of electricigens can be evaluated by a high-throughput colorimetric assay based on the extracelluar dye reduction.It was proved that high polar dyes including of MO and NGB,which were not able to enter cells and only reduced extracellularly,could be used as the snesors for evaluating the exoelectrogenic ability of electricigens.Through monitoring extracellular dye decolorization under anaerobic conditions,this plate-based photometric assay could not only rapidly measure the exoelectrogenic ability of various electricigens and but also distinguish the electron release capacities among different mutants.Furthermore,the exoelectrogenic ability of mixed bacterial community in microbial fuel cells?MFCs?was successfully coupled with the extracellular dye decolorization,implying that this method could not only apply to pure strains,but also be suitable for mixed communities.In addition,this method could be performed to optimize the carbon source,temperature and other operation conditions to increase the exoelectrogenic efficiency.Thus,this novel high-throughput colorimetric evaluation method established in this study was a simple,convenient,accurate,reliable and multifunctional method.