Effects of three biological agents on intestinal microbiota of white shrimp (Litopenaeus vannamei) in a water-recirculating cultivation system

Abstract:

[Objective] We studied the effects of three biological agents on intestinal microbiota and immunity of white shrimp (Litopenaeus vannamei) in a water-recirculating cultivation system.[Methods] The composition of three biological agents were Bacillus subtilis, Candida utilis, nitrifying bacteria and photosynthetic bacteria (treatment 1); Proteinase, Acidophilus spp., Bacillus subtilis and Faecalis spp. (treatment 2); and Protease, yeast, Bacillus subtilis and Lactobacillus acidophilus (treatment 3). After feeding 30 days, the total numbers of bacteria and Vibrio in the intestine of L. vannamei were calculated using plate counting. The high throughput sequencing of 16S rDNA gene's V3+V4 region was used to determine diversity and composition of bacterial communities. Real time fluorescence quantitative PCR was used to analyze the expression levels of Toll-like receptor 1 (TLR1) and Dorsal.[Results] After the application of biological agents, the total number of bacteria in the intestine of L. vannamei was reduced to 7.22 CFU/g, and the growth of Vibrio was inhibited (5.01 CFU/g) in treatment 3. In treatment 3, the percentage of high sequences and Operational Taxonomic Unit (OTU) were increased to 98.8% and 326, Chao1, Simpson, Shannon was 581.34, 0.94, 5.52 respectively, which displayed the changes of bacterium abundance and diversity in intestine. Furthermore, the community structure of intestinal microbiota was optimized. Proteobacteria, Bacteroidetes, Actinobacteria, Verrucomicrobia, Firmicutes, Candidatus Saccharibacteria and Cyanobacteria were the main dominant phyla. However, the proportion of Bacteroidetes was significantly increased (40.7%) in the treatment 1 (P<0.05). The different expression levels of Toll-like receptor 1 and Dorsal were changed in different probiotics. In treatment 3, the expression level of Toll-like receptor 1 (TLR1) was 3.2 (P<0.05), which was 220% higher than control, meanwhile, the expression level of Dorsal was 4.7 (P<0.05), which was 370% higher than control.[Conclusion] Our study revealed that biological agents played an active role in the recirculating system, which could optimize the structure of intestinal microbiota and improve the expression levels of immune genes. In this case, these biological agents could serve as candidates for diseases prevention and healthy aquaculture. And the treatment 3 was the better.