Study On Broadening The Spectrum Of Available Substrate In Shewanella Oneidensis MR-1

Microbial electrocatalytic systems based on electroactive microorganisms are a new generation of technologies for controlling environmental pollution and developing new green energy sources with broading application prospects.However,the limited spectrum of available substrate in exoelectrogens limited their practical applications.In this paper,from the aspects of strengthening acetate utilization to improve the cells’coulombic efficiency and constructing the―Klebsiella pneumoniae-Shewanella oneidensis”consortium to utilize cellulose hydrolysate for bioelectricity,greatly directly or indirectly broaden the spectrum of available substrate in Shewanella oneidensis MR-1.The main research results are as follows:1.Engineering S.oneidensis utilizing acetate to produce bioelectricity:Firstly,to enable S.oneidensis to consume acetate as the sole carbon source for harvesting bioelectricity in microbial fuel cells(MFCs),we used molecular biology strategies to successfully construct three genetically recombinant S.oneidensis(Ace U1,Ace U2,and Ace U3)by assembling the succinylacetate coenzyme A transferase genes ato1 and ato2 from Geobacter sulfurreducens and citrate synthase gene glt A from S.oneidensis,respectively.The results revealed the engineered Ace U3 could produce the maximum power density(8.3±1.2 m W/m~2)with acetate as substrate.In addition,Ace U3 enabled a maximum electricity power density of 51.0±3.1 m W/m~2and the coulombic efficiency reached 12.4%with lactate as substrate,which is2.4-folds and 2.0-folds compared with the control strain,respectively.The results show that the coulombic efficiency can be enormously improved by reconstructing the TCA cycle and acetate utilization pathway.2.The construction of consortium utilizing cellulose hydrolysate for bioelectricity:Firstly,to produce more lactate in K.pneumoniae,we eliminated the ethanol and acetate pathway via deleting pta(alcohol dehydrogenase gene)and adh E(phosphotransacetylase gene).Furthermore,to construct a synthesis and delivery system,we further expressed ldh D(lactate dehydrogenase gene)and lld P(lactate transporter gene).Lastly,to facilitate extracellular electron transfer(EET)of S.oneidensis,a biosynthetic flavins pathway from Bacillus subtillus was expressed in a highly hydrophobic S.oneidensis CP-S1,which not only improved direct-contacted EET via enhancing S.oneidensis adhesion to the carbon electrode but also accelerated the flavins-mediated EET via increasing flavins synthesis.Thus,under the optimization conditions,the recombinant consortium generated a maximum power density of 104.7±10.0 m W/m~2,which was 7.2-folds and 2.2-folds higher than that of the wild-type and knockout consortium,respectively.Furthermore,we used this synthetic microbial consortium in the corn straw hydrolyzates-fed MFC,obtaining a power density 23.5±6.0 m W/m~2.The results show that the construction of consortium system is an effective strategy to indirectly broaden the spectrum of available substrate in exoelectrogens.