Construction Of Artificial Cell Walls And Their Regulation On The Collective Behaviors Of Unicellular Organisms

In recent years,cell surface engineering technology has received extensive attention from researchers.Researchers have modified various kinds of materials to the cell surface through different kinds of means to form artificial cell walls,achieving the goals of regulating the properties and functionalities of cells,and improving the viability of cells when facing harsh environments.The as-generated cell-in-shell structure has great potential in the field of cell storage,green energy,immunotherapy,biosensors,etc.However,the current research in the field of cell surface engineering mainly focuses on the protection and the regulation of existing properties and functions of cells.There are few reports on the interaction between individual cells and cell populations,especially the influence of changes in the properties and functions of individual cells on the collective behaviors of cell populations.The Study on the influence of artificial cell walls on the properties and functions of cell populations is of great scientific significance for further understanding the interaction mechanism of cell populations and expanding its application range.In this paper,a variety of materials and methods were used to construct artificial cell walls with diverse properties and functions on the cell surface to explore the effects of changes in the properties and functions of individual cell properties on the behavior of cell swarms.The main research contents are as follows:A polymer-based artificial cell wall was constructed based on photo-induced electron transfer reversible addition-fragmentation chain transfer polymerization（PET-RAFT）,which achieved the modification of cell properties at the single cell level and the regulation of cell function in the cell swarm.The chain transfer agent（CTA）was modified on the surface of Chlorella by the reaction of mercaptothiazoline with amino groups in the cell wall(2.1×10⁷μm^-2).The molecular weight of the PMAEB block could reach 31000 g/mol after the cationic monomer dimethylaminoethyl methacrylate quaternary ammonium salt（MAEB）was polymerized under 460 nm blue light for 6hours.The obtained polymer has a narrow molar mass distribution,which shows that the polymerization in this system proceeded in a controlled manner.The constructed Chlorella with positively charged artificial cell walls can aggregate with negatively charged native Chlorella cells to form aggregates of about 200 microns.Due to the shading effect inside the aggregates,the respiration of the internal Chlorella cells was stronger than photosynthesis,thereby forming an anaerobic environment inside the aggregates and activating the hydrogenase in the Chlorella cells,which then allowed a functionality switching of the encapsulated Chlorella cell from the normal photosynthetic O₂ production towards H₂ production and last for 42 hours.The average H₂ production rate of the constructed aggerates was 0.26μmol H² h^-1（mg chlorophyll）^-1,which is 1.3 times faster in comparison to the instantaneous biomass-to-fuel yield in nature.On the basis of successfully regulating the function of the cell swarm,an artificial cell wall with catalytic activity was further constructed on the cell surface.In combination with the proliferation process of unicellular organisms,the constructed artificial cell wall endows the encapsulated cells with motion ability that they do not inherently possess.Accordingly,by taking advantage of the emergence of differentiated moving abilities,we achieve the self-sorting between mother cells and daughter cells in a proliferated Saccharomyces cerevisiae（S.cerevisiae）cell community.This part of the work used aldylated mesoporous silica nanoparticles（MSNs-CHO）as a"bridge"to immobilize urease on cells（S.cerevisiae,S.pombe and Chlorella）to build catalytically active artificial cell wall.The modification content of urease on the surface of yeast cells can reach 5.44×10^-18 mol/μm²（S.cerevisiae）and 4.3×10^-18 mol/μm²（S.pombe）.By controlling the proliferation time,the asymmetric coating of the artificial cell wall on the cell surface was achieved.The asymmetric distribution of urease on the cell surface could generate an asymmetric local electric field and electroosmotic flow around the cell,which successfully endows the cells with the motion ability that they don’t initially possess.The maximum velocity of S.pombe（4.5μm/s）was twice that of S.cerevisiae（2.15μm/s）.The effects of urea concentration,proliferation time,and cell proliferation mode on individual and swarm movement behavior of cells were explored by analyzing the velocity of cells.Furthermore,by taking advantage of the motility differences between the mother cells and daughter cells in the S.cerevisiae system,the self-sorting of mother cells and daughter cells was realized in a microchannel in the presence of urea.On the basis of successfully regulating the function of the cell swarm,endowing cells with the ability that they do not inherently possess,and realizing the self-sorting behavior in the cell swarm,a light-responsive artificial cell wall was further constructed on the cell surface to endow the cell swarm with the ability to respond to the external environment.Titanium dioxide with aldehyde group（Ti O₂-CHO）and polypyrrole（PPy）was used to construct a light-responsive artificial cell wall on the surface of S.cerevisiae.By detecting the degradation rate of titanium dioxide and polypyrrole complex（Ti O₂-PPy）on Rhodamine B solution,the optimal modification time for assembling polypyrrole was determined to be 4 hours.The maximum photocurrent density can reach 4.7μA/cm²(Light intensity,20 m W cm^-2).The collective behavior of Saccharomyces cerevisiae cells coated with light-responsive artificial cell walls（S.cerevisiae@Ti O₂@PPy）in different media（water,hydrogen peroxide solution,ferrocene methanol solution）was summarized by analyzing the cell movement behavior.The swarming negative phototaxis migration behavior of S.cerevisiae cells in ferrocene methanol solution was realized(0.26μm/s,10 m W cm^-2)and the mechanism of the light-controlled cluster behavior was proposed and verified by analyzing the motion behavior in different concentrations of MFc.The universality of the light-responsive artificial cell wall was further proved by exploring the collective behavior of Ti O₂ and PPy-coated Chlorella,which provided a new strategy for the regulation of cell collective behavior.