Characteristics Of Typical Algal Surface Coat And Its Influence On Transfer Of Matter

Surface coat is a structure widely found around the cells of microorganisms,plants and animals.Algal surface coat is not only a physical barrier between algal cells and the surrounding environment,but also a defense against adverse environmental factors such as ultraviolet radiation,toxic compounds,drying,predation of zooplankton,etc.It also provides a microenvironment of essential nutrients and trace elements.In addition,surface coat is involved in a series of processes such as intercellular interaction,adhesion and aggregation,which enables algae to form a strong ecological competitive advantage,thus forming a bloom.At present,a lot of researches focus on the influence of external influence factors on the yield of surface coat and the surface coat contribution of formation of algal colonies.However,the mechanism of the role of surface coat as a bridge between algal cells and the external environment,especially in the aspect of material transfer,has not been fully clarified.Based on this background,16 cyanobacteria and green algae with different surface coat morphology were selected in this study,and the extraction methods of algal surface coat were summarized in the past 10 years.The main factors affecting the extraction effect of surface coat were summarized.The influence of surface coat on the algal substance transfer was discussed,and different temperature pulse conditions were applied to understand the response mechanism of surface coat under temperature stress.The main research results are summarized as follows:（1）Different morphologies of surface coat were optimized by extraction methods.Two factors and orthogonal experiments were carried out on different kinds of algal surface coat（slime,capsule and sheath）by centrifugal method,ultrasonic method,cation exchange resin method,hot water extraction method,sulfuric acid water bath method and sodium hydroxide water bath method.The results showed that the extraction effect was not obvious under the mild treatment conditions（centrifugal method and cation exchange resin method）.Soluble polysaccharides（RPS）are secreted into the surrounding environment,and RPS can be collected by filtration.The slime was completely extracted by sodium hydroxide water bath（0.01 mol/L NaOH,50-70℃,10-30 min）.The capsule was completely extracted by sulfuric acid water bath（1 mol/L H₂SO₄,50-70℃,20-40 min）.The sheath was mainly treated with sodium hydroxide water bath（0.01 mol/L NaOH,80℃,40 min）and ultrasonic method（ice bath,20 KHz,≥30 W,on 3 s/off 3 s,≥2 min）.（2）Characteristic analysis of different morphologies of surface coat.The polysaccharides and proteins secreted by algae are mainly bound to the surrounding algal cells.A small part（<50%）is secreted into the external environment.The monosaccharides and amino acids are significantly different in different layers,indicating that surface coat are heterogeneous.The difference the hydrophobicity and the location of deoxidized sugar would increase the hydrophobicity of slime.The results of principal component analysis showed that the proportion of RPS acid amino acids（aspartic acid,glutamic acid）is greater than slime.The proportion of the hydrophobic amino acid（valine）in slime was higher than RPS or the difference was not large.Therefore,the difference of the hydrophobic in slime and RPS was from fucose,rhamnose,aspartate,glutamic acid and valine.The ratio of glucuronic acid in RPS or slime was higher than that in the capsule of the same algae.The proportion of hydrophilic amino acids（glycine,threonine）in slime is higher than that in the capsule,so the difference between the more easily hydrated and more hydrophilic is glucuronic acid,galactoacuronic acid,glycine and threonine.The proportion of glucuronic acid（glucuronic acid,galactohyuronic acid）in the sheath is lower than that in the capsule,and the hydrophobic amino acid proportion of the sheath is relatively stable,while the hydrophobic amino acid proportion of the capsule fluctuates greatly,so the capsule is more adhesive than the sheath.The reason why the sheath is hydrophobic lies in the glucuronic acid and hydrophobic amino acid.（3）The effect of surface coat on the absorption of algal cell material.Results show that the surface coat has a certain degree of enrichment of nutrient substance,capsule and sheath combined with algal cells,sticky capsule makes the capsule is more efficient than sheath to nutrient enrichment,and slime and algal cells combined loosely,and easy to hydration,lead to weak nutrient enrichment,resulted different morphologies surface coat on the absorption rate of NH₄⁺mainly for capsule>sheath>slime.The presence of surface coat increased the absorption of NH₄⁺and the release of O₂ of algal cells,and the influence degree of different morphologies surface coat on the material flux was different.The influence degree of algal surface coat on NH₄⁺flux was sheath>capsule>slime.The degree of influence of surface coat on O₂ flux was capsule>sheath>slime.The surface characteristics of different morphologies surface coat are different,which affect the diffusion rate of substances,and to a certain extent,regulate the transfer conditions of nutrient elements inside and outside the cell,and accelerate the mutual transfer of substances.（4）The effect of surface coat on the transfer of algal cell material by temperature pulse.Under the heat stimulation,algal cells all changed from oxygen release to oxygen consumption,and the oxygen release rate of algal cells increased significantly under the cold stimulation.The same algal colonies have similar response time to temperature stimulation,in general,respond to stimuli time was capsule 450 s>slime 300 s>sheath200-300 s,the algal cells after remove surface coat is largely shorten the response time of external stimuli.It shows that the surface coat has a certain buffering effect on the external temperature stimuli and the buffering effect is different in different morphology.