Toxic Effects Of Sulfide On The Pacific White Shrimp,Litopenaeus Vannamei

Sulfide is a natural and widely distributed toxicant.It can be commonly found on the interface between water and sediment in the aquatic environment.The Pacific white shrimp Litopenaeus vannamei starts life in the benthic zone soon after the mysis stage,an early stage of post larvae.Therefore,L.vannamei is inevitably affected by exposure to sulfide released from pond sediment.The toxicity and poisoning mechanisms of sulfide were studied in Litopenaeus vannamei from the perspective of energy metabolism and metabolomics.The lethal concentrations of sulfide in L.vannamei(LC50)at 24 h,48 h,72 h,and 96 h were determined.Sulfide at a concentration of 0,1/10(425.5?g/L),and 1/5(851?g/L)of the LC50 at 96 h was used to test the metabolic responses of L.vannamei for 21 days.The chronic exposure of shrimp to a higher sulfide concentration of 851?g/L decreased shrimp survival but did not affect weight gain or the hepatopancreas index.The glycogen content in the hepatopancreas and muscle and the activity of hepatopancreas cytochrome C oxidase of the shrimp exposed to all sulfide concentrations were significantly lower,and the serum glucose and lactic acid levels and lactic acid dehydrogenase activity were significantly lower than those in the control.Metabolomics assays showed that shrimp exposed to sulfide had lower amounts of serum pyruvic acid,succinic acid,glycine,alanine,and proline in the 425.5?g/L group and phosphate,succinic acid,beta-alanine,serine,and 1-histidine in the 851?g/L group than in the control.Chronic sulfide exposure could disturb protein synthesis in shrimp but enhance gluconeogenesis and substrate absorption for ATP synthesis and tricarboxylic acid cycles to provide extra energy to cope with sulfide stress.Chronic sulfide exposure could adversely affect the health status of L.vannamei,as indicated by the high amounts of serum n-ethylmaleamic acid,pyroglutamic acid,aspartic acid and phenylalanine relative to the control.This study indicates that chronic exposure of shrimp to sulfide can decrease health and lower survival through functional changes in gluconeogenesis,protein synthesis and energy metabolism.This study also explored the toxicant effect of different concentrations of sulfide on the intestinal health and microbiota of the white shrimp by monitoring the change of expression of inflammatory,immune related cytokines,and the structure of the intestinal microbiota.The gut histology,expressions of inflammatory and immune related cytokines(tumor necrosis factor-alpha,C-type lectin 3,myostatin and heat shock transcription factor 1),and the microbiota were determined in L.vannamei after exposure to 0(control),425.5(1/10 LC 50-96 h),and 851?g/L(1/5 LC 50-96 h)of sulfide for 21 days.With the increase of sulfide concentration,intestinal injury was aggravated and the inflammatory and immune related cytokines generated a range of reactions.The expression of myostatin(MSTN)was significantly down-regulated by the concentration of sulfide exposure.No difference in the expression of heat shock transcription factor 1(HSF1)was found between the control and shrimp exposed to 425.5?g/L,but significantly higher HSF1 expression was found in shrimp exposed to 851?g/L of sulfide.Significantly higher values of tumor necrosis factor-alpha(TNF-?)and C-type lectin 3(CTL3)were found in the shrimp exposed to 425.5?g/L of sulfide compared to the control,but a lower value was found in the shrimp exposed to 851?g/L(P<0.05).Sulfide also changed the intestinal microbial communities.The abundance of pathogenic bacteria,such as Cyanobacteria,Vibrio and Photobacterium,increased significantly with exposure to the increasing concentration of sulfide.The abundance of some anti-stress bacteria,such as Chlorobi and Fusobacterium,increased.Nitrospiraewhich can alleviate nitrite toxicity decreased.Microbacterium,Parachlamydia,and Shewanella were all commonly found and down-regulated in both sulfide groups,which is associated with an adaptation to sulfide stimulation.This study indicates that chronic exposure to sub lethal levels of sulfide could lead to damage of the gut structure,stimulate the response of the inflammatory and immune systems,and shape the structure of the gut microbiota in L.vannamei.