Semiconductor-mediated Extracellular Electron Transport Of Microorganisms Under Light Excitation

The extracellular electron transfer mechanism of microorganisms is an important process of energy transfer and conversion.Adequate electron donors in the environment ensure the completion of the microbial electron transport chain and bring about a continuous redox reaction through this mechanism.This electron transfer mechanism of microorganisms also plays an important role in the geochemical cycle and environmental remediation.In addition to autotrophic microorganisms absorb energy in the environment to meet their own metabolism and reproduction,some non-autotrophic microorganisms can also obtain light energy to meet their energy needs through semiconductor minerals.These light-sensitive semiconductor materials convert solar energy into chemical energy through photocatalysis to support and stimulate the growth of microorganisms.In our study,we are committed to discovering the response relationship between microorganisms and semiconductor materials,further exploring the impact of photo-generated electrons on microbial flora.In order to study which bacteria in the flora may use light energy through semiconductor minerals,and the effect of photocatalysis on the structure and diversity of the flora,four groups of microbial fuel cells were constructed,in which pure carbon paper and carbon paper modified with semiconductor materials were used as anode electrodes.At the sametime,fill the soil from the environment in the anode chamber of the microbial fuel cell as the source of flora.After three operating cycles,16SrRNA gene sequencing of the microorganisms flora on the electrodes under photocatalytisis conditions was carried out.From the analysis results,we found that semiconductor materials have a very significant impact on the microbial species abundance and species diversity.Photo-generated electrons are important factors affecting microbial communities.At the same time,bacteria were picked and purified from the anode electrode of the device which modified with Fe₂O₃.After16SrRNA sequencing analysis,3 strains with semiconductor responsiveness were obtained.In order to explore the difference on using light energy through semiconductors between different non-autotrophic microorganisms,six kinds of bacteria were used for this research.The role of semiconductor materials in the extracellular electron transfer process was reflected by the electrochemical characterizations,including output power density,CV curve,i-t curve and so on.At the same time,the microorganism whether has the ability to use light energy through semiconductor materials was judged.According to the results,we find that not all the non-autotrophic microorganisms have the ability to use light energy through semiconductors.There is a certain specificity between microorganisms with this ability and semiconductors.Klebsiella can obtain light energy through three semiconductor materials,while Citrobacter,Rhodococcus and E.maltophilia can only use light energy through one semiconductor material,while Bacillus lysine and Bacillus cereus cannot use light energy through semiconductors.At the sametime,Bacillus cereus and Rhodococcus that these two Gram-positive bacteria strains have the ability to secrete redox substances to mediate extracellular electron transfer was confirmed.I-t was confirmed that the redox substances secreted by the two strains were RF and FMN through the determination of the redox peak position of the CV curve and the analysis of the HPLC spectrum,and the concentrations of the two redox substances were related to the bacterial growth curve.Flavins can interact with electron acceptors to promote the transfer of electrons and further promote the growth and metabolism of bacteria as endogenous electron shuttles.These results indicated that the indirect extracellular electron transport mechanism mediated by electron shuttle mediators is the main electron transport mode of the two Gram-positive strains involved in our experiments.Our research proves that some non-phototrophic microorganisms could use specific semiconductor materials to accelerate the extracellular electron transfer process under photocatalytic conditions and convert solar energy into chemical energy through photosensitive semiconductor materials as energy for its own metabolism at the same time.Such a system will provide a unique driving force for the biochemical redox reaction on the surface of the earth.