The Mechanism Of Pyruvate On The Activation Of Palladium Reductionin In Shewanella Oneidensis MR-1

Shewanella oneidensis MR-1 is a model strain of the electrochemical active bacteria because of its strong capability of extracellular electron transfer(EET)and genetic tractability.In this study,we investigated the effect of carbon sources on EET in S.oneidensis MR-1 using reduction of palladium ions(Pd(?))as a model.Studied from this work was carried out mainly from two aspects.For one hand,the regulation of pyruvate on Pd(?)reduction was investigated.On the other hand,the effects of different carbon sources on energy level were studied.Besides,a transposon library was constructed,and will be used to screen the pyruvate sensing regulator.The specific research results are obtained as follows:(1)Compared with lactate,the reduction of Pd(?)was significantly accelerated by pyruvate as carbon source in S.oneidensis MR-1.Moreover,acceleration was positively relates to a preincubation time with pyruvate and initial concentration of pyruvate,suggesting that the acceleration was involves in a hierarchical regulation.This rapid reduction of Pd(?)not only protects the bacteria from Pd(?),but also greatly improves the synthesis rate of palladium nanoparticles.(2)The transcriptome sequencing and real-time fluorescence quantitative PCR analysis revealed significant upregulation of formate dehydrogenase,Mtr pathway,DMSO respiratory pathway,and hydrogenase transcription after S.oneidensis MR-1was preincubated with pyruvate.The enhanced pyruvate catabolism and electron transfer explained the acceleration effect of pyruvate on Pd(?)reduction.Finally,the reporter gene analysis of the expression of[Ni-Fe]hydrogenase Hya AB showed that the expression of[Ni-Fe]hydrogenase Hya AB was also positiviely correlated with initial concentration of pyruvate and the preincubation time.Such a result consistent with the effect of pyruvate on Pd(?)reduction.(3)To investigate whether pyruvate preincubation would affect S.oneidensis MR-1 reduction of Pd(?)from the energy levels Compared with lactate,pyruvate did not change the intracellular content of NADH and NAD~+,as well as the ratio of[NADH]/[NAD~+].At the same time,there was no significant difference in membrane potential between different carbon sources.Therefore,it is concluded that the accelerated effect of pyruvate on Pd(?)reduction dosen't involve in energy metabolism.(4)A transposon library of S.oneidensis MR-1 was constructed with a capacity of 200 000 mutants.For subsequent screening of regulatory factors that participate in pyruvate sensing and regulate downstream gene expression to enhance Pd(?)reduction.Reduction of Pd(?)by microbia is a promising strategy for the simultaneous reduction of palladium and synthesis of nano-palladium.In this work,the effect of pyruvate on Pd(?)reduction and underlying mechanism were investigated,which is benefit for futher improvement of the performance of S.oneidensis MR-1 in Pd(?)reduction.