Research On The Mechanism Of Extracellular Electron Transfer Of Rhodopseudomonas Palustris

Microbial electron transfer is one of the basic processes of microbial metabolism,which drives the transformation of matter and energy.With the deeper understanding of the mechanism of microbial electron transfer,it has been widely studied that the application of bioelectrochemical technology in multiple fields(including energy conversion,environmental remediation,biosynthesis).Among them,electrochemical active microorganisms,including archaea,bacteria and fungi,are the biological basis of bioelectrochemical systems.Photosynthetic bacteria are a kind of photoautotrophic electrochemically active microorganisms,which can use CO2 as carbon source and produce value-added chemicals.How to effectively regulate the CO2 conversion of photosynthetic bacteria is one of key scientific questions in the field of chemical engineering.From the perspective of microbial electron transfer,this thesis selected a model bacterium of photosynthetic bacteria,Rhodopseudomonas palustris CGA009,as the research object,and discussed the extracellular electron transport mechanism of R.palustris CGA009,using bioelectrochemical technology and proteomics technology.It would provide a theoretical support for regulating its application in environment field.The main research contents are listed as follows:(1)The redox characteristics of R.palustris CGA009 were profiled by cyclic voltammetry.The results showed that R.palustris CGA009 cells had redox ability,and could secrete redox-active molecule during incubations.The redox-active molecule was identified as riboflavin by High performance liquid mass spectrometry(HPLC-MS)which could be further photodegraded to lumichrome with redox-activity under photostimulation.As a novel discovered electron shuttle,lumichrome can significantly enhance the metabolic rate of R.palustris CGA009.(2)A three-electrode system was constructed to study the CO2 reduction performance of R.palustris CGA009 under different potentials(-0.8 V,-0.5 V,-0.2 V vs.Ag/AgCl).The results showed that R.palustris CGA009 reached a highest efficiency at-0.8 V,and the maximum current density was 175 mA/m2 with the CO2 consumption rate 21.1 mg/(L·d-1).(3)To further explore the extracellular electron transport mechanism of R.palustris CGA009 under different potentials.Differentially expressed proteins of R.palustris CGA009 were compared between potential-dependent groups and control groups,using the label-free proteomics technique.There are three main results:Part of proteins located on the cell membrane such as cytochrome c oxidase and ABC transporter were significantly up-regulated at-0.5 V and-0.8 V,which might involve the process of electron transfer in the transmembrane;Gene ontology function enrichment of differentially expressed protein mainly included independent ATP periplasmic transport complex,light collection complex and plasma membrane light collection complex,etc.Based on KEGG pathway,most of differentially expressed proteins existed in the pathway of ATP transport.Based on the analysis of the differentially expressed proteins with cathodic potentials,the proteins related to light capture and ATP synthesis and conversion were significantly up-regulated at-0.8 V.Therefore,the microbial electron transfer of R.palustris CGA009 during CO2 fixation mainly depends on the synthesis pathway of ATP.