Regulation Of Nitric Oxide Signal On Aquacultured Sea Cucumber (Apostichopus Japonicus) Subjected To New Pathogenic Bacteria Challenge

Apostichopus japonicus,as an important economic species of mariculture,has been growing in scale in recent years due to its unique nutritional and medicinal value.However,the frequent occurrence of skin ulceration syndrome in artificial cultured sea cucumber has seriously restricted the healthy development of sea cucumber aquaculture.As a marine benthic echinoderm,sea cucumber has a unique immune defense mechanism,Therefore,in the face of the frequent occurrence of "skin ulceration syndrome",the key to solve the problem is to improve the immune adaptability of Apostichopus japonicus.Nitric oxide is an important signaling molecule,nitric oxide signaling system is widely involved in animal immune defense and anti-infection.Therefore,it is of great practical significance to study the regulation of nitric oxide signaling system in immune defense of Apostichopus japonicus for the prevention and treatment of skin ulceration syndrome of cultured Apostichopus japonicus.In this study,the taxonomy and growth characteristics of three pathogenic bacteria from skin ulceration syndrome of sea cucumber were analyzed by microbiological methods.The results show that eleven pathogenic bacteria isolated from skin ulceration of cultured sea cucumber,among these,the three dominant pathogenic bacteria were S.saprophyticus,S.haemolyticus and S.epidermidis,and the fatality rate were all one hundred percent.Therefore,Staphylococcus is an important pathogen which can cause skin ulceration syndrome of sea cucumber.In order to compare the toxicity of three pathogenic bacteria,analyzed the characteristics of the strains and the immune defense and anti-infection ability of sea cucumber.The results show that,the incidence,severity and incidence index of Staphylococcus haemolyticus infected Apostichopus japonicus were the highest and the body weight was the lowest,and it also can cause significant changes of systemic immune enzymes activity of Apostichopus japonicus.Oxytetracycline and tetracycline,commonly used antibiotics,had the weakest bacteriostatic effect on Staphylococcus hemolyticus,The effects of temperature,salinity and pH on the biofilm formation of Staphylococcus haemolyticus were significantly different.Therefore,the pathogenicity of Staphylococcus hae,molyticus is strong,which can cause systemic immune stress response of Apostichopusjaponicus.In order to explore the role of nitric oxide signaling system in immune defense of Apostichopus japonicus,analyzed the changes of cellular immunity,humoral immunity and related immune gene expression The results show that,nitric oxide(NO)content,total nitric oxide synthase(tNOS)activity and inducible nitric oxide synthase(iNOS)activity,acid phosphatase(ACP)activity,superoxide dismutase(SOD)activity,lysozyme(LZM)activity,complement C3 activity,cell activity,respiratory burst activity and phagocytic activity,as well as complement C3(Ajc3)and lysozyme gene relative expression in intestinal tissue and body wall muscle tissue in Apostichopus japonicus treated with sodium nitroprusside(NO donor)was higher than that of control group.Compared with the Apostichopus japonicus treated with Staphylococcus haemolyticus,the NO signal content,cellular immune activity,humoral immune enzyme activity and immune gene expression of Apostichopus japonicus treated with NG-nitro-L-arginine(NOS inhibitor),decreased.Therefore,NO signal participates in the process of immune defense and anti-infection of Apostichopus japonicus.At the same time,sodium nitroprusside can effectively improve the content of NO and the activity of NOS in Apostichopus japonicus,thus improving the immune defense ability of Apostichopus japonicus.