Abstract:Immune response of Litopenaeus vannamei fed with biofilm and planktonic cells of Bacillus cereus was studied by evaluating the growth rate, disease resistance and intestinal microflora. The biofilm and planktonic cells of B.cereus (PC465) were added to original feed as biofilm feed and planktonic feed respectively. Shrimps were maintained in 24 buckets with similar lighting and position in three groups. Biofilm group and planktonic group were fed with the concentration of 108 CFU/g of either biofilm or planktonic cells added feed for 15 d. Shrimps were challenged with white spot syndrome virus (WSSV) after 17 days post feeding in both experimental diet groups. Then a reverse gavage challenge with Vibrio parahaemolyticus has been tested on day 22. The growth rate of shrimp was evaluated on day 1, 5, 10, 15. The diversity and composition of bacterial communities of shrimp intestine were assessed by high throughput sequencing of 16S rDNA on day 1, 5, 10, 15, 20 and 25. The results showed that the growth rate and final weight of the biofilm group and the planktonic group were higher than the control group. The intestinal microflora of L.vannamei mainly consisted of Proteobacteria, while Bacteroidetes, Actinobacteria, Firmicutes, Verrucomicrobia, Cyanophyta, with the content of Proteobacteria accounting for about 94%. The proportion of Firmicutes in the shrimp intestine of the biofilm group (0.45%) and planktonic group (0.93%) was higher than the control group (0.02%). Proteobacteria mainly included Vibrio, Photobacterium, Pseudoalteromonas, etc. The proportion of Vibrio in the biofilm group, planktonic group and control group was 34.65%, 39.27%, and 58.00%, respectively. The cumulative mortalities of the biofilm group, planktonic group and control group challenged with WSSV were 80%, 77% and 92%, respectively. The cumulative mortalities of the biofilm group, planktonic group and control group challenged with V. parahaemolyticus were 61.3%, 75% and 77.3%, respectively. It is concluded that diet supplemented with B. cereus can change the intestinal microflora of L.vannamei, improve the disease resistance and enhance growth. The biofilm fed shrimps were more resistant to virus Vibrio and pathogens compared to that with planktonic fed and the control shrimps.
