Studies On The Secretion And Adhesion Action Of Extracellular Polymeric Substances From Marine Benthic Diatoms

In marine ecological system, marine benthic diatom is a kind of important microalge. As the main primary producers, they play an important role in the global carbon cycle. However, marine benthic diatoms are main member in the field of marine biofouling. They do great harms to marine artificial engineering facilities and marine environment by attaching on varities of surfaces underwater. Marine benthic diatoms attach on surfaces of artificial facilities by secreting numbers of extracellular polymeric substances(EPS), then they become the main component of microfouling biofilm and apply convenient condition to macrofouling. The extracellular polymeric substances from marine benthic diatoms are the important material basis of studing on the diatom fouling mechanism. By studing on the secretion and adhesion action of EPS, it helps to discuss the diatom attachment mechanism, and develop new skills and methods of control the attachment of diatoms.The water-soluble and water-insoluble components in EPS from marine benthic diatoms were extracted by hot solvent method in this paper; the phenol-sulfuric acid method was employed to measure the content of polysaccharide and the Coomassie Brilliant Blue G-250 method was employed to measure the content of protein in the extractions.we measured and quantified the EPS from single cell to investigate the secretion change of EPS at different growth cycle and the content differences of EPS from different species of diatoms. The results showed that the contents of EPS were different with the different cell density for Navicula pinna at different growth cycle. In the same growth area, the more cell density, the more the number of cells, the less the contents of EPS, and the less contents of polysaccharide and protein. It indicated that the secretion action of EPS changed with the changes of different growth cycle. And the contents of polysaccharide was obviously higher than protein at the whole growth cycle(p<0.05). At the exponential stage, the cell growth rates of diatoms(Navicula leavissima, Navicula parva, and Navicula pinna) were different, then the cell densities were different on the same growth condition, so the contents of EPS from three species of diatoms were different.But the percentages of all components in EPS had nothing to do with diatom growth cycle and species. The percentages had no obviously change(p>0.05).The environmental factors had directly impacts on the composition and secretion action of EPS from diatoms. So the effects on oxygen contents and attachment areas for secretion action of EPS were discussed in this paper. The cell numbers of diatoms under different environmental factors were measured through the method of blood cell counting plate and UV spectrophotometry, and the contents of all components in EPS from diatoms were quantitied. The results showed that the growth rate was faster and the content of EPS in single cell was more under the environmental conditions of higher oxygen content and bigger attachment area. Compared to the oxygen content, the attachment area had less impact on the growth rate of diatoms and secretion contents of EPS.Lastly, the infiltration characteristics were studied between EPS from diatoms and four kinds microstructures silica gel materials to investigate the adhesion action on the material surfaces. The thetas were measured between different concentration of water-soluble and waterinsoluble EPS and four kinds microstructures silica gel materials by The Attention Theta. The results showed that the concentraction of EPS had impact on the infiltration characteristics between EPS from diatoms and material surfaces on the same material surface. The higher concentraction of EPS, the smaller theta between solution and material surfaces, then the bigger the infiltration characteristics, the stronger the characteristics of attachment. The filtration characteristics between the same concentraction of EPS and different microstructures silica gel materials depended on the roughness of material surfaces. The more rough the surfaces, the bigger thetas between EPS solutions and surfaces, then the smaller the filtration characteristics, the weaker the characteristics of attachment. And the filtration characteristics between water-soluble component and material surfaces was stronger than water-insoluble components.