The Study Of Bacterial Disease Of Cultured Caulerpa Lentillifera And Laminaria Hyperborea In China

Seaweed industry is an indispensable and important part of fishery.The seaweed culture not only plays an important role in food supply,but also has remarkable ecological service function.The rapid development of seaweed breeding industry has brought considerable economic benefits to mariculturists.According to the 2017 China Fisheries Statistical Yearbook,the national seaweed aquaculture production is22,350,012 tons,and the total amount of seaweed cultured and processed accounts for more than 70%of the world,making it the largest seaweed farming country in the world.The frequent occurrence of algal diseases is one of the bottlenecks for the healthy development of algae industry.The research on the diseases of important large-scale economic algae such as Laminaria and laver has made important progress.However,the research on some emerging economic alga,such as ferns from Caulerpa lentillifera and Laminaria hyperborea,is still in its infancy.This paper focuses on the bacterial diseases of two emerging large-scale economic algae(Caulerpa lentillifera and Laminaria hyperborea)in the breeding process.This paper systematically analyzed the black brown disease of Caulerpa lentillifera,which was outbreaked in July 2017 in a farm in Dalian,and a white spot disease of Laminaria hyperborea that broke out in March 2018.The pathogenic bacteria were isolated and identified,and the pathogenicity of the pathogen was determined by the test of back infection,and the histopathological analysis was carried out at the same time.Which provided a useful reference for the prevention and control of bacterial diseases in the long-stem fern and the northern kelp.1.Etiology of cultured Caulerpa lentillifera black brown diseaseThe clinical symptoms of the disease are:The whole lesion was black and brown,the hand felt soft and sticky in the algal body,the stolons with severe infection were obviously dark black and brown,and the top algal body was ulcerated.A dominant strain CL2017070801002 was isolated from the diseased algae,and the bacterial solution with a concentration of 10~3-10~8 CFU/m L was used to soak the infected Caulerpa lentillifera.Within 7 days,different degrees of dark brown typical symptoms were observed in the algae bodies of each infected experimental group.The results of artificial infection experiment showed that CL2017070801002 was pathogenic to Caulerpa lentillifera.Scanning electron microscopy(SEM)showed that a large number of bacteria were accumulated on the surface of the cell wall of the algae,and the cell tissue was destroyed and died with the extension of the infestation time.The results of the study indicate that CL2017070801002 is the pathogen of Caulerpa lentillifera black brown disease.By combining Gram staining,physiological and biochemical characteristics and 16S r DNA sequence phylogenetic tree analysis,the bacterial strain was identified as Vibrio alginolyticus.The results of drug sensitivity test showed that the strain was highly sensitive to chloramphenicol,tetracycline,fleroxacin,doxycycline and flufenicol,and moderately sensitive to gentamicin,clarithromycin and other drugs,but to penicillin and cephalosporin,cefradine and other drugs are not sensitive.According to the disease and pathogenic characteristics of the disease,the disease was named as Caulerpa lentillifera black brown disease,which provided a useful reference for the prevention and control of bacterial diseases of Caulerpa lentillifera.2、Etiology of leukoplakia in cultured Laminaria hyperboreaThe clinical symptoms of the disease are:From brown to light brown,severe parts appear transparent white,until the formation of plaque,and the surface becomes pleated.A dominant strain LH2018030802002 was isolated from the diseased algae,and the bacterial solution with a concentration of 10~3-10~8 CFU/m L was used to soak the infected Laminaria hyperborea.Within 7 days,the algal bodies of each infected experimental group showed different degrees of typical symptoms of leukoplakia.The results of artificial infection experiment showed that LH2018030802002 was pathogenic to Laminaria hyperborea.The microscopic section observation of paraffin tissue showed that there were obvious differences in the degree of damage of various tissues after Laminaria hyperborea is infected by Pseudomonas alternans.The results show:The most severely damaged tissues in the algae body were endothelial cells,followed by the outer cortex and medulla,while the surface damage was less severe.Ultrastructural pathological studies showed that the infection of pseudomonas alternans with different concentrations had different effects on Laminaria hyperborea to different degrees.Scanning electron microscopy(SEM)showed that a large number of bacteria formed mucus on the surface of the cell wall of the algae body.With the prolongation of the infection time,the cell tissue ruptured and died.The results of transmission electron microscopy(TEM)showed:In the algae body,chromatin was the most sensitive organelle of alginate-degrading bacteria,followed by nucleus.In contrast,the more stable organelles are mitochondria.Chlorophyll fluorescence results show that:compared with control group,the maximum fluorescence yield(Fv/Fm)of photosystem II,the maximum photochemical quantum yield(Fv’/Fm’)of light-adapted leaves,and the potential activity of photosystem II reaction center,which decreased significantly with the increase of infection concentration.It shows that the donor side of blade optical system and the activity of reaction center systemic suppression by pathogen infection.These findings indicate that LH2018030802002 is the pathogen of Laminaria hyperborea leukoplakia found.By combining Gram staining,physiological and biochemical characteristics and 16S r DNA sequence phylogenetic tree analysis,the bacterial strain was identified as Pseudoalteromonas sp.The results of drug susceptibility test showed that the strain was highly sensitive to drugs such as chloramphenicol,bactericidal,azithromycin,ofloxacin and florfenicol,and moderately sensitive to drugs such as lomefloxacin and doxycycline.However,it is not sensitive to penicillin,neomycin,tetracycline,cephalosporin,kanamycin,cefazoxime,compound neomycin and other drugs.According to the disease and pathogenic characteristics of the disease,the disease was named as Leukoderma of Laminaria hyperborea,which provided a useful reference for the prevention and control of bacterial diseases of Laminaria hyperborea.The research on large-scale seaweed diseases in China is still very weak.This paper focuses on two new large-scale economic algae-Caulerpa lentillifera and Laminaria hyperborea.At present,it is in the initial stage of development in China,It is also necessary to deal with the problems of disease and miscellaneous algae control technology in the field of deep science and technology.Therefore,in order to reduce the losses caused by diseases in the seaweed culture process,it is very important to study the etiology and epidemiology of large-scale economic seaweed.