Formation And Regulation Mechanisms Of Conditioning Layer And Biofilm During Marine Biofouling

Marine biofouling is a complex phenomenon,causing a series of serious problems.It is therefore important to prevent or alleviate biofouling by taking effective measures.However,due to the thousands of species of marine organisms and the complex nature of the biofouling process,it is a great challenge to develop antifouling methods with long-term effectiveness,broad-spectrum antifouling property,and repairability.Extensive research efforts have been devoted to developing antifouling techniques.However,to achieve these,it is essential to understand at molecular level the formation behaviors of conditioning layer and biofilm and their underlying mechanisms.As the first stage participating in biofouling process,adsorption of molecules plays critical roles in mediating formation of biofilm.This thesis investigates the adsorption behaviors of typical protein and polysaccharide,albumin and alginate,on arc-sprayed aluminum coatings and their influence on adhesion of Escherichia coli.The adsorption of the molecules is characterized by infrared spectrometry and atomic force microscopy.Results show that the adsorption inhibits effectively adhesion of the bacteria.Further investigation suggests that adsorbed alginate/albumin alteres the hydrophilicity/hydrophobicity and electronegativity of the coatings instead of impacting on the survival of the bacteria to decline their adhesion.However,both alginate and albumin dramatically promotes adhesion of Bacillus sp.,Chlorella and Phacodactylum tricornutum.This is attributed to gradually enhance biological impact by the presence of the molecules involved in the biofouling.It is evidenced that alginate and albumin supply as carbon source for the microorganisms for the reinforced adhesion.A variety of factors play important roles in regulating the adhesion behaviors of microorganisms.This project systematically examined the influence of Ca²⁺and Mg²⁺in artificial seawater on attachment and colonization of Bacillus sp.,Chlorella and Phaeodactylum tricornutum on silicon wafer.The typical divalent cations in culturing solution give rise to significantly enhanced adhesion of the microorganisms.Mg²⁺and Ca²⁺affect the adhesion of Bacillus sp.primarily by regulating aggregation and formation of extracellular polymeric substances.The ions altere quantity and types of the proteins in extracellular polymeric substances,in turn affecting subsequent adhesion.However,it is noted that Mg²⁺promotes adhesion of Chlorella predominately by regulating extracellular polymeric substances formation and in particular polysaccharide synthesis.Ca²⁺plays a more important role in protein expression to enhance the adhesion of Chlorella.For Phaeodactylum tricornutum,Ca²⁺expedites protein synthesis for enhanced adhesion.It is known that alginate actively takes part in fouling and biofouling.Alginate-related biofouling relies on its ability to form bonds by binding divalent cations.In this project,negative-staining electron microscopy was employed for the first time to characterize the structure of alginate and the conformations of the egg-box junctions after its binding with calcium/copper ions.After recruitment of divalent calcium ions to form calcium alginate,unusual tangling of the alginate chains is clearly seen,giving rise to formation of spiral conformation of exaggerated egg-box assembly.The conditioning layer comprising calcium alginate remarkably promotes the colonization of the typical bacteria and diatoms.However,interaction of copper ions with alginate mitigates their toxicity to marine microorganisms by decreasing the concentration of copper ions in the solutions.Based on the clarification of the mechanisims relating to the conditioning layer and biofilm,surface modification of aluminum coatings was made through altering their physichochemical properties.The coatings with specially designed micro-/nano-hybrid structures were constructed and exceptional topographical morphologies were successfully produced by post-spray steam sterilization processing at 120^oC.The porous needle-like nanostructures show the oxide grains of 250 nm in length and 60nm in width in-situ grown on the surfaces of the coatings.The in-situ growth of the top alumina layer with the unique nano-patterns on aluminum coatings together with the micro topography of aluminum formed during the spraying give rise to a unique micro-/nano-hybrid structure.The structure offer the coatings excellent capability to inhibit effectively the adhesion of marine alga Chlorella and Phaeodactylum tricornutum.In addition,textured antifouling surfaces with quaternary ammonium salt were also prepared by self-assembly method.The samples show exciting antifouling performances.The approaches proposed in this research are effective in investigating formation mechanisms at molecular level of marine macromolecules and the results gained from this research shed some light on effective ways of modifying materials surfaces for desired antifouling performances.