Electron Acceptors Globally Regulate The Metabolism Of Shewanella Decolorationis

Microbial respiration plays an important role in various natural biogeochemical processes and engineered biosystems.It was extensively reported that the substrate diversity and metabolic efficiency of microorganisms vary according to the electron acceptors.In theory,the free energy available for microbial metabolism should increase with electron acceptor redox potential?EARP?.Therefore,it is generally considered that EARP is a determining factor for microbial metabolism.However,it is challenging to study the relationship between EARP and microbial metabolism activity,as the naturally existing electron acceptors contain other different physicochemical properties,which may also affect the microbial metabolisms.The solid electrode with accurately poised redox potential in microbial electrochemical system?MES?provides an ideal tool for investigating the regulation of EARP on microorganisms.In recent years,the influence of EARP on microbial community,pollutants degradation and certain genes or pathways have been studied.However,no comprehensive and systematic regulation information of EARP on microbial metabolism was reported.Furthermore,electron acceptors usually coexist in various environments,while most reported microbial studies were conducted with only one kind of electron acceptor which is far to understanding the microbial processes in real environment.In this study,MES methods,RNA sequencing technology and Shewanella decolorationis S12?S12?which could respirate with diverse electron acceptors,were used to study the global regulation of electron acceptor physicochemical characteristics and coexistence on S12 metabolism.Main conclusions were summaried as follows:Firstly,EARP globally regulates transcriptomic profiling in Shewanella decolorationis S12.MES and transcriptomic methods were used to analyze the global regulation of different EARP?-0.2,0.2 and 0.8 V?on the metabolism of strain S12.Results demonstrated that the metabolic activities of strain S12 showed nonlinear response to EARP.Genes involved in energy production,amino acid syntheses and transportation,carbon metabolism and lipid metabolism pathways showed EARP specificity,while no key extracellular cytochrome c in electron transport chain such as MtrABC showed significant difference between different EARPs.The energy intensive flagella assembly and assimilatory sulfur metabolism pathways were significantly enriched at 0.8 V?MES0.8?,which suggested that strain S12 had stronger electrokinesis behavior and oxidative stress-response at high EARP.The tricarboxylic acid?TCA?cycle for central carbon metabolism was down-regulated while glyoxylate shunt was up-regulated in MES0.8 compared to 0.2 V?MES0.2?and-0.2 V?MES-0.2?.Those results provide the first global information of EARP regulations on microbial metabolism.Moreover,the results also suggested that EARP is an important but not the only determinant for metabolic pathways of strain S12.Secondly,EARP and the other physicochemical properties of electron acceptor regulated different metabolic pathways of S12.Transcriptomic profiles of S12 respiring with the ubiquitous actual electron acceptor O2?0.8 V?and electrodes?MES0.8 and MES0.2?were compared,to further study the regulation of the physicochemical characteristics other than redox potential of electron acceptors on S12 metabolism.Results showed that the substrate metabolic activity of MES0.8 and MES-0.2 was significantly lower than aerobic respiration.Transcriptomic profiles and metabolic pathways analysis showed that the other physiochemical porperites of electron acceptor had greater influence on S12 metabolism than EARP.The activity of complete TCA cycle,amino acid synthesis and cell synthesis pathways were higher under aerobic condition,while amino acid degradation pathway was enriched in MES0.8 and MES-0.2.It can be speculated that amino acid degradation metabolism is one of the most important way for S12 to harvest energy in MES0.8 and MES-0.2.The enrichment degree of complete TCA cycle pathway was much higer under aerobic condition than in MES-0.2,which demonstrated that partial carbon source was oxidized through complete TCA in MES-0.2.Genes in sulfur metabolic pathway were significantly up-regulated under aerobic condition than in MES0.8,which confirmed the supposition that sulfur assimilation metabolism is an important oxidative stress response for S12 at high EARP conditions.It further revealed the role of different physicochemical characteristics of electron acceptor?including redox potential,solubility and so on?in regulating S12 metabolism.Thirdly,the metabolic pathway of S12 being globally regulated by coexist electron acceptor is the fundamental reason of higher electricity production but lower amaranth degradation.The regulatory mechanism of two coexisting extracellular respiratory electron acceptors regulating on S12 metabolism had been studied.Amaranth,an azo dye with strong polarity and electrode which have similar redox potential were used as soluble and solid extracellular respiratory electron acceptors for S12.It was demonstrated that the expression of chemotaxis methyl receptors signaling proteins,carbon metabolism and cytochrome c genes were significant different with electrode and amaranth as electron accetors.Moreover,gene expression profiling of S12 with coexistence of amaranth and electrode,showed higher similarity to the expression profile of S12 respiring with electrode,with some genes in oxidative phosphorylation were differently regulated,which may be associated with electricity generation of S12.Furthermore,according to the RNA sequencing data and gene functional identification analysis,gene SHD₂784 was similar with sulfite oxidase gene and first found to be specific to S12 electrogenesis capacity but not to amaranth reduction.The above results suggest that,the solubility and molecular structure of extracellular electron acceptors could significantly affect S12 metabolism.When multiple electron acceptors coexisted,S12 would prefer to respirate with a certain one,but the other ones also have effects on its metabolism.In conclusion,this study provided the first systematical and global regulation of electron acceptor physicochemical properties and coexist electron acceptor on S12 metabolism and revealed the regulation mechanism.Moreover,a novel important electrode respiring gene of S12 was found.Those findings,on one hand,gave new insights into the complex regulation of electron acceptor on microbial metabolism,which supplemented and improved the basic theoretical knowledge of bacterial respiratory metabolism;On the other hand,had important guiding significance for the optimization of microbial technologies such as bioremediation and MESs.