The Preliminary Study On Mechanism For Probiotic Effects Of Lactobacillus Plantarum In Litopenaeus Vanname

In this paper, Litopenaeus vannamei, Pacific white shrimp,a precious southern coastal important economic breeding species,is object of the study. A 15-day feeding trial was conducted indoor to explore the effects of dietary Lactobacillus plantarum supplementation in three different doses and four treatments on the growth, digestive enzymes activities, intestinal morphology, composition of the intestinal flora, and nonspecific immunity of white shrimp. Base on the result, we explored the mechanism for probiotic effects of L. plantarum in L. vannamei.A 15-day feeding trial was conducted to investigate the effects of dietary L. plantarum additives at a rate of 0, 0.5%, 1% and 2% supplementation on the growth, digestion, digestive enzyme activities, and intestinal morphology of juvenile white shrimp(initial weight, 8.10 ± 0.13 g). Results showed that there were significantly higher final body weight, weight gain rate, and specific growth rate and significantly lower feed conversion rate in 0.5% and 1% groups than those in the control group(P<0.05). Close contact exists between growth and nutrient digestion and absorption. The shrimp fed the diet containing 0.5% L. plantarum had significantly higher digestive enzyme activities in the hepatopancreas and gut. Under conditions of an optical microscope level, the shrimp fed the diet containing 0.5% L. plantarum had significantly higher enterocyte height than the shrimp fed the control diet(P<0.05). In conclusion, dietary L.plantarum at optimal supplemental level of 0.5% led to improve the growth performance, activities of digestive enzymes and gut morphology of Pacific white leg shrimp. The findings can provide technical support and experimental basis in the effective use of L.plantarum in shrimp culture.In the present study, the effect of dietary of L. plantarum in different treatments on the growth performance, digestive enzyme activity and gut morphology of juvenile Pacific white shrimp, L. vannamei were studied. Four diets supplement, including fermentation supernatant(FS), live bacteria(LB), dead bacteria(DB) and cell-free extract(CE) of L. plantarum were fed to shrimps for 15 days. In comparison to the control group, final weight was significantly improved in FS, DB, and CE group(P < 0.05). The maximum weight gain rate(WGR) and specific growth rate(SGR) of the CE diet group were significantly higher than that of other groups(P < 0.05), followed by DB, FS and LB diets groups, and finally the control diet. The FCR of CE diet group was lower than that of the control, LB, DB and FS diets groups(P < 0.05), but was not significantly different in FCR of the LB, DB, and FS diet groups(P > 0.05). The highest digestive enzymes activity(amylase, lipase and pepsin activity) in the hepatopancreas and gut of shrimps was observed in the CE diet group. Histology study revealed that dietary CE diet could significantly increase the enterocytes height of shrimp. These results indicate that the administration of cell-free extract of L. plantarum could improve the growth performance, digestive enzymes activity and gut morphology of L. vannamei.A compare study was conducted to investigate the effects of dietary L. plantarum in different treatments on non-specific immunity of L. vannamei and indicators measured including immune enzyme activities: phenoloxidase(PO), acid phosphatase(ACP), malondialdehyde(MDA) and immune gene expression: Toll mRNA and superoxide dismutase(SOD) mRNA. The results showed PO activity in the hepatopancreas and gut of shrimp in the DB and CE diet groups were significantly higher than that in the control group(P < 0.05), while ACP activity in the hepatopancreas and gut of shrimp in all treatment diet groups were significantly higher than that in the control group(P < 0.05). MDA activity in the hepatopancreas and gut of shrimp in other treatment diet groups, except LB diet group, were significantly lower than that in the control group(P < 0.05). In the hepatopancreas and gut, dietary L. plantarum in four different treatments supplementation significantly increased mRNA expression of Toll mRNA and SOD mRNA than those in the control group. These results indicate that the administration of CE or FS of L. plantarum could improve non-specific immunity of L. vannamei.The intestinal community composition of L. vannamei and interactions between microbial species response to dietary L. plantarum in different treatments supplementation was measured through Illumina HiSeq platform based on bacterial 16 S DNA V3-V4 region, and the shrimps with the basal diet served as the control group. The dominant phyla in all groups were Proteobacteria, Bacteroidetes, and Verrucomicrobia. Specifically, the dominant microbial flora of L. vannamei in all groups were γ-Proteobacteria, and α-Proteobacteria, but the relative abundance of them were different from each other. The relative abundance of γ-Proteobacteria, and α-Proteobacteria in LB diet group and the control group were similar, and whose relative abundance were 68%, 66%, and 10%, 11%, respectively. The γ-Proteobacteria(57%), and α-Proteobacteria(20%) were the predominant class in the FS diet group. A significant increase in the relative abundance of α-Proteobacteria(23%) and Verrucomicrobiae 11%) was shown in the DB diet group, following with sharp decline in the relative abundance of γ-Proteobacteria(46%). The γ-Proteobacteria(mainly classified as Alteromonadales) was the predominant class(increased to 78%) in the CE diet group.