A Preliminary On The Protection Effects Of Lactobacillus Pentosus HC-2 On Penaeus Vannamei Against Aflatoxin B1

To investigate the positive effect of Lactobacillus pentosus HC-2 on protecting the Penaeus vannamei affected by AFB1 toxicity.Shrimp were respectively fed with formulated feed containing AFB1,AFB1+L.pentosus HC-2,and a basal commercial diet.After feeding for 6 weeks,the survival and growth,the changes of histology morphology,gene expression and enzyme activity of the hepatopancreas and the changes of histology morphology,gene expression and intestinal flora of the intestine of P.vannamei were determined.To explore the effects of L.pentosus HC-2 on the hepatopancreas morphology,immune-related genes and enzyme activity of P.vannamei affected by AFB1,shrimp were respectively fed with formulated feed containing AFB1(500μg/kg),AFB1(500μg/kg)+L.pentosus HC-2(5×10~8 CFU/g feed),and a basal commercial diet(Control group).After feeding for 6 weeks,the survival rate(AFB1 group:37%,AFB1+L.pentosus HC-2 group:49%,Control group:61%)and the percent weight gain(AFB1 group:98.28%,AFB1+L.pentosus HC-2 group:112.40%,Control group:111.27%)in the AFB1+L.pentosus HC-2 group were higher than the AFB1group.At the end of the experiment,the hepatopancreas morphology,the expression of immune-related genes,and the activity of hepatopancreas enzymes were detected.The hepatopancreas morphology of the AFB1+L.pentosus HC-2 group suffered less damage than the AFB1 group.The relative expression of immune-related genes(Rab,GST,mucin-like PM,Dorsal,Relish,Pro–PO)in AFB1 group and AFB1+HC-2group was significantly lower than control group(P<0.05),and the relative expression of immune-related genes(GST,Dorsal,Pro-PO)in AFB1+HC-2 group was higher than the AFB1 group(P<0.05).The activity of Alkaline Phosphatase(AKP)increased significantly in AFB1 group and AFB1+HC-2 group compared with the control group,and the activity of AKP in AFB1+HC-2 group was higher than the AFB1 group.The activity of Glutathione S-Transferase(GST)increased in AFB1group and AFB1+HC-2 group compared with the control group,and there have no significant difference in AFB1+HC-2 group and AFB1group.The activity of Superoxide Dismutase(SOD)and Catalase(CAT)has no significant difference between the AFB1 group and AFB1+HC-2 group,and the Total Antioxidant Capacity(T-AOC)has no significant difference between the control group and the experimental group.We concluded that L.pentosus HC-2 had a positive effect on the hepatopancreas structure of shrimp stimulated by AFB1,and induced a significant effect on some immune genes and AKP activity,but had no significant effect on the T-AOC of the hepatopancreas.The intestinal morphology of AFB1+HC-2 group was less damaged than that of AFB1 group.The relative expression of immune-related genes including Rab,GST,mucin-like-PM,Dorsal,Relish and Pro-PO was detected.Expression of most immune-related genes in the experimental group significantly decreased compared with the control group,while the expression levels of immune genes(Rab,GST,mucin-like-PM,Dorsal and Pro-PO)in AFB1+L.pentosus HC-2 group was higher than the AFB1 group,but there was no significant change in Relish gene expression between the control group and the experimental group.Intestinal microbiota analysis demonstrated that the community structure of intestinal microbiota was obviously different between the control group and experimental group.There were 440 OTUs in the three groups,among which 522 were the least in the control group,AFB1+HC-2group had the most unique OTUs(862 OTUs).Among the three groups,Proteobacteria,Firmicutes,Bacteroidetes and actinobacteria were the most abundant.At the phylum level,the relative abundance of Proteobacteria in AFB1+HC-2 group increased significantly compared with the control group,while the relative abundance of Firmicutes and Bacteroides decreased significantly.At the genus level,The abundance of the intestinal microbiota in the experimental group changed greatly at the genus level compared with the Control group.The relative abundance of Photobacterium and Vibrio in the AFB1+HC-2 group increased compared with the Control group,while the relative of Acinetobacter,Desulfobulbus,and Oscillospira decreased.The relative abundance of Oscillospira and Ruminococcus in the AFB1group increased compared with the Control group,while the relative abundance of Acinetobacter and Desulfobulbus decreased.Desulfovibrionales was the most significant difference in the intestinal flora of group AFB1,and lactobacillus was the most significant difference in AFB1+HC-2 group.These results indicated that L.pentosus HC-2 had a positive effect on the growth performance and resistance of P.vannamei affected by AFB1 according to regulate the structure of intestinal flora.In breeding practice,probiotics can be used to reduce the harm of aflatoxin.This may be related to the probiotic’s contribution to maintaining the structural integrity of the intestinal mucosa,promoting the expression of immune related genes and regulating the composition of intestinal microflora.It was concluded that the effect of L.pentosus HC-2 on regulating the imbalance of intestinal flora of P.vannamei affected by AFB1 was not obvious,but it reduced the content of some bacteria representing an unhealthy state.This change may be related to the reduction of shrimp mortality when challenged by AFB1.The results provide data support for further study on the mechanism of L.pentosus HC-2 reducing AFB1 toxicity,and provide scientific theoretical basis for probiotics in the healthy culture of P.vannamei and other aquatic organisms.On the other hand,the mechanism of probiotics weakening the toxicity of aflatoxin remains to be further verified.For example,whether probiotics degrade aflatoxin directly or by adjusting the intestinal microflora,or whether they neutralize the toxicity of aflatoxin or directly activate the immune activity of the host,remains to be elucidated.