Chemically Synthesized Nano-CdS Mediates Shewanella Oneidensis MR-1 Photoautotrophic Carbon Fixation Research

The rapid consumption of fossil energy and the continuous emission of carbon dioxide and other energy and environmental problems have promoted the development of advanced technologies for solar energy utilization and carbon dioxide fixation.The construction of a semi-artificial photosynthetic system combines the high selective catalytic ability of microorganisms with the strong light conversion efficiency of semiconductors,and can fix CO₂while realizing the conversion of solar energy to chemical energy.Shewanella oneidensis MR-1（MR-1 for short）as an electrochemical model strain has strong electron uptake ability and carbon fixation metabolism potential,and is a potential strain for carbon fixation in a semi-artificial photosynthetic system.In our previous research,MR-1 has been The photoautotrophic fixation of CO₂to produce acetic acid was shown to be mediated by biodeposited CdS.Acetic acid can be further upgraded into high-value products by other microorganisms.In contrast,biological cadmium sulfide mediated MR-1 acetate production at lower levels.In view of this situation,this study carried out a systematic study on the enhancement of the photoautotrophic carbon fixation ability of MR-1 mediated by exogenous addition of chemically synthesized CdS.By synthesizing and adding CdS with different nanostructures,CdS nanospheres were preferred to combine with MR-1 to construct a photoautotrophic carbon fixation system;the ability of CdS nanospheres to mediate MR-1autotrophic carbon fixation was verified,and the system carbon fixation conditions were optimized.A huge increase in long-term acetic acid production was achieved;the electron transport pathway and sulfur cycle process in the photoautotrophic process were studied,and the carbon fixation metabolic pathway was revealed in combination with genomics analysis.The main research contents and conclusions of this paper are as follows:（1）The MR-1@CdS photoautotrophic carbon fixation system was initially constructed.Chemically synthesized CdS nanoparticles with three different nanostructures:nanospheres,nanorods,and nanosheets.The nanospheres in CdS with the same hexagonal crystal system have better excitation ability and electron-hole separation rate than nanorods and nanosheets.By combining CdS with different nanostructures with MR-1,the nanosphere system can produce 0.217m M acetic acid after 3days of photoautotrophic reaction,which is 5.3 times that of the nanosheet system and 1.83 times that of the nanorod system.（2）The photoautotrophic ability of MR-1@CdS was systematically analyzed and optimized.MR-1 increased the biomass by 58%in the presence of CdS and light for 7 days.The cells lacking light and CdS gradually died because they could not be autotrophic.CdS is loaded and redeposited on the bacterial surface,and plays an important role in mediating the acquisition of light energy.By optimizing the inoculum amount and CdS load,the optimal inoculum and CdS load were determined as OD₆₀₀=0.4 and CdS=0.1m M,respectively.After optimization,the cell proliferation reached 200%in 20 days of continuous light,and the acetic acid yield reached 3.13 m M in 20 days.With the help of day and night simulated light experiments,it was found that the autotrophic production of acetic acid was also accompanied by heterotrophic consumption.（3）The inorganic-organic interface bonding mode and electron transfer process between CdS and MR-1 during the photoreaction were analyzed.MR-1 obtains photoelectrons from CdS through direct electron transfer,and its electron transfer mode is transformed from free flavin-mediated to c-type cytochrome-bound flavin-mediated mainly,and obtains a stable and gradually enhanced photoelectron during the photoreaction process.photocurrent.The addition of endogenous sulfur sources such as S₂O₃^2-and S^2-,SO₃^2-can be used as a hole sacrificial agent to be oxidized to SO₄^2-under the action of photogenerated holes,and at the same time,it forms the S cycle in vivo with sulfur reduction and respiration,which ensures the system for a long time.Cell activity and metabolic capacity provide the basis.Combined with genome analysis,it was concluded that the carbon fixation pathway matched with MR-1 was the seventh carbon fixation pathway,"reduced glycine pathway".37 Figures,7 Tables and 118 References...