Study On The Isolation, Identification And Toxicity Of Pathogenic Bacterium Isolated From Juvenile Haliotis Discus Discus

The pathogenic bacterium was isolated from the diseased juvenile Haliotis discus discus,and confirmed to be toxic pathogenic strain by recursive infection experiments;the physiological and biochemical characteristics,classification and identification of pathogenic strain,and its drug sensitivity to antibiotics common used in aquiculture were studied.The extracellular toxic substances excreted by pathogenic strain were separated and purified and the virulent factor in them was preliminarily disussed.This study had a significance that it can prevent and cure the disease of juvenile Haliotis discus discus,improve survival rate of juvenile of Haliotis discus discus,promote the development of abalone aquaculture.Through the experiments,the results were as follows:The pathogenic strain was isolated from the diseased juvenile of Haliotis discus discus and preliminarily identified as Sphingomonas by its morphology,physiological and biochemical experimental results based on .The strain was ulteriorly identified as Sphingomonas paucimobilis with the help of BD PhoenixTM - 100 identification system of FuJian Center For Disease Control&Prevention.The confidence value is 99%.The growing characteristics of Sphingomonas paucimobilis were as follows:the growth curve was radically identical in solid and liquid culture media,It beginned its logarithmic phase after 6h,reach maximal biomass at 24h and enter death phase after 36h.Its suitable growing conditions were:pH7～8,salinity2～3%, 30℃,and c 100r/min.It grows better in seawater. The toxic substances of Sphingomonas paucimobilis were studied and the results showed that it could excrete toxin protein during growth period and the relationship between biomass and excretion of toxin protein is isochronous.The drug sensitivity to antibiotics common used in aquiculture was studied and the results showed that the strain is highly sensitivity to Rifampin,PolymyxinB,Sulfamethoxazole/Trimethoprim,Norffoxacin,Nalidixic,but resistant to CephazolinV,Streptomycin,Kanamycin,Amikacin,Gentamicin,Doxycycline,Ceftriaxone.So the highly sensitive drug could be choosen to prevent and cured the disease of juvenile Haliotis discus discus..The extracellular products of Sphingomonas paucimobilis were obtained by using cellophane plate culture technique.The crude exotoxin was obtained by ammonium sulfate sedimentation and heated at 80℃for 30 minutes.The healthy juvenile Haliotis discus discus artificially infected by those substabces all died and the results showed the exotoxin was highly toxic and thermo-stable.The exotoxin was separated and purified by DEAE-cellulose anion exchange chromatography..Two protein peaks were obtained,which could cause healthy juvenile of Haliotis discus discus to die by artificial infection.