Research On Properties Of Exocelluar Envelope Of Algae Based On Atomic Force Microscopy

In recent years,blue-green algae blooms have been occurring frequently in the upper reaches of the Yangtze river,which has a very huge influence on the water environment ecology,as well as on human production and life.In the researches on the occurrence mechanism of algae bloom,the physiological and ecological characteristics of blue-green algae have become the research hotspots in global.Studies showed that the exoeelluar envelope of algae ean provide a barrier of protection to eells in harsh conditions,enhance the competitiveness of algae among phytoplanktons,and play a role of bridge in the outbreak of bloom for being the key structure joining single cells to form colonies.This study aims to complete the method and content system of researches on the properties of envelope of algae,explain the reason why cyanobacteria and chlorophyta had become the dominant algaes in lake-reservoir ecosystem from the perspective of the natural physiological function of envelope,and provide basic theory for the the study of blue-green algae bloom's generation and maintenance mechanism.In this study,We introduced atomic force microscopy(AFM)into the study of properties of exocellular envelope of algae,completed the experimental process in dectecting the surface of envelope of algae in-situ by AFM force spectroscopy and built a completed set of analysis method for the force-displacement curves of algae,which including three models of Pincus theory,Hertz-Sneddon model and Hooke's law.This method was used to study the physical properties(gel thickness and structural hierarchy)and biomechanical properties(interfacial elasticity,surface adhesion and water retention rate)of envelope in different morphology(sheath/capsule).In this study,AFM experiments were carried out on eell surfaces of algae with different morphologieal envelopes.At the same time,optical microscopy and flow cytometry were utilized in this study for more investigation about the physical properties of different algae cells(colonies)with envelopes in different morphology under different cell cycle composition conditions including envelope thickness,size of cell(colony),ratio of envelope thickness and the cellular(colonial)equivalent diameter.Twelve strains of cyanobacteria and chlorophyta with different morphological envelopes were selected as experimental subjects in this study,and the main conclusions were as follows:(1)The capsule was generally more elastic and adherent than the sheath surface,and the capsule-containing algae cells were more easy to gather.The sheath was generally more water-repellent than the capsule,and the sheath-containing algae cells were more difficult to deform under the external force of the water body.The structural stratification of the envelope varied from the algae species and was not significantly related to the morphology of the gel(sheath/capsular).(2)The thickness of the less elastic envelope was changed in synchronism with the growth and division of the cells;while the thickness of the more elastic envelope was stable under different cell cycle compositions.The envelopes of the algal cells in the DNA synthesis or division phase were thicker than of the algal cells in the DNA haploid state.(3)In the proeess of eolony formation,the sheath·covered algae cells were mainly aggregated by dividing,while the capsule-coverd algae cells were mainly aggregated by adhering.