Pathogenicity Difference Of Different Photobacterium Damselae Subsp.damselae Strains To Sebastes Schlegelii

From 2016 to 2018,a large number of explosive diseases occurred in the deepwater cage cultured Sebastes schlegelii in Changdao China,and the main pathogen of the outbreak of this disease have been confirmed as Photobacterium damselae subsp.damselae(PDD)by using pathogenic pathology methods and artificial infection tests.In order to know more about PDD,we have choose 25 strains of PDD which are from different sources in pathogen bank,and analyze their phenotypic characteristics,virulence gene delivery and transcriptome analysis of S.schlegelii infection with different strains of PDD.(1)Only 2 strains showed beta hemolysis,the others 23 strains showed alpha hemolysis.All 25 strains showed resistance to 5 antibiotics of Amikacin,Streptomycin,SMZ-TMP,Acetylspiramycin and Oxacillin,and susceptivity to 6antibiotics of Nalidixic acid,Fleroxacin,Cetriaxone Sodium,Cefotaxime,Ceftizoxime and Lomefloxacin.The differences of drug susceptivity existed in the others 27 antibiotics including Enrofloxacin and so on.The MIC of these 25 strains were almost the same to 2 antibiotics of Nalidix acid and Ciprofloxacin,but significant difference to 3 antibiotics of Polymyxin B,Ofloxacin and Lomefloxacin.This study confirmed that the phenotypic characteristics of PDD strains which isolated from different host and region were significantly different.(2)Presently,the host which infected by PDD is often accompanied by hemorrhagic septicemia,as a result of that,the main researches are hemolysin-related genes carried by PDD.In this study,three hemolysin coding genes were selected which are hly,dly and hlyA,we also choose a gene encoding hemolytic phospholipase,plpV,and a virulence gene which encode collagenase,co?P.The result of agarose gel electrophoresis of PCR amplified products is as follows: Among 25 strains of PDD,25 strains carry hly gene,24 strains carry hlyA and plpV genes,only 2 strains carry dly gene,and 9 strains carry co?P gene.The two strains of PDD which carry the virlent gene dly show the strongest hemolysis ability which is called betahemolysis.The result of artificial infection experiments shows that there are differences in pathogenicity among different strains.(3)After assembled with TRINITY software,the total transcript number is236210,the total unigene number is 199502,and the length range of transcripts is mainly between 0-500 bp,accounting for about 63%,a total of 126303.After annotating the unigene by GO?NR?KEGG?Pfam?COG and Swiss-Prot data base,there are 22960?53358?46197?49800?22280 and 61148 unigene have been annotated.GO and KEGG enrichment analysis of differential expressed genes shows that the genes related to immune response and biological metabolism showed significant changes.At the same time,cell adhesion,various cell surface receptors and signal transduction pathways shows significant changes.The number of differential expressed genes annotated to immune-related pathways in the virulent strain group is more,and the number of genes annotated is more too.The number of immune-related pathways annotated in the lentogen strain group is less,and the number of related genes is also less.