Experimental Study On Adhesion Mechanism Of Two Marine Benthic Diatoms

Marine benthic diatom is an important kind of unicellular eukaryotes in marine ecosystem.They usually attach on the shallow sea seafloor,intertidal zone,rocks and animals and plants surface,as well as artificial facilities,and they may cause great harms to marine artificial engineering facilities as one of fouling organisms.Marine benthic diatoms attach on substrate surfaces by secreting extracellular polymeric substances.The growth and secretion of extracellular polymeric substances of benthic diatoms are significantly affected by light,temperature,salinity and nutrient.Benthic diatoms are sensitive to the changes of environmental factors.Different benthic diatom species have different growth characteristics,biochemical compositions,attachment forms,attachment substrate and control factors.At present,the research on the mechanism of marine benthic diatom attachment is limited,especially the relationship between attachment behavior and environmental factors and the physiological response is relatively weak.The study of the mechanism of the benthic diatom has important theoretical and practical significance for the study of marine benthic ecosystem and fouling organisms.Two common marine benthic diatoms,Achnanthes javanica var.subconstricta(MMDL5271)and Nitzschia closterium(MMDL50319)isolated from Xiamen coastal waters were used in this study.We measured the content of intracellular protein and polysaccharideand the content of protein,polysaccharide,uronic acid and sulfate in different components of extracellular polymeric substances in different salinity,light intensity,nitrogen,and phosphorus and silicon concentration,andthe adhesion ratioof two diatoms under the different conditions.The results show that the growth rate,Ch1 a content and polysaccharide and protein content of two diatoms could maximat when salinity was 30,light intensity was 50?mol·m·s-1,concentrations of N,P,Si were 7.69,0.65,3.36 mg/L,respectively.It was advantageous for the extracellular polysaccharide under high light intensity 250 ?mol·m-2·s-1 and high N concentration 76.9 mg/L,and low P concentration 0.065 mg/L can stimulate the production of intracellular polysaccharide,and high P concentration 6.5 mg/L was positive for the attachment of diatoms.The influences of environment conditions on productions of biochemical compositions were species specific.There were many differences between the two diatoms in attachment methods and adhesion ratio.Achnanthes javannica var.subconstricta attached by stalk,and the adhesion ratio maintained at a high level(30.36%-32.96%)in the experiment.Nitzschia closterium directly attached by valve,and the adhesion ratio increased gradually as the cell density increase(from 1.14%to 6.24%).The adhesion ratio of the two diatoms was decreasedobviously(Achnanthes javanica var.subconstricta 16.21%,Nitzschia closterium 3.51%)in late experiment.There was a positive correlation between the cntent of uronic acid in extracellular polymeric substances and the adhesion ratio in early experiment.The result of the adhesion ratio of Achnanthes javanica var.subconstricta on three common building materials under different light conditions was polymethylmethacrylate>glass>stainless steel,full light shading>shading from bottom>no shading.The adhesion ratio of Achnanthes javanica var.subconstricta was higher on the hydrophobic substrate and in darkness,and bottom light generates an obvious inhibition on its attachment.