Application of bacterial lipopolysaccharide to improve survival of the black tiger shrimp after Vibrio harveyi exposure.

This study investigates an effect of bacterial lipopolysaccharide (LPS) as feed supplement to improve immunity of the black tiger shrimp (Penaeus monodon). LPS was coated to commercial feed pellets and given to the shrimp once or twice a day for 10 days before an exposure with shrimp pathogenic bacterium Vibrio harveyi. The growth rates, percent weight gains, total hemocyte and granulocyte counts and survival rates of shrimp between the LPS-coated pellet fed groups and a control group where shrimp fed with commercial feed pellets were compared. After 10 days of the feeding trials, growth rates were not significantly different in all groups, suggesting no toxicity from LPS supplement. To determine beneficial effect of LPS diets, each group was subsequently exposed to V. harveyi by immersion method and the survival rates were recorded for seven days after the immersion. Regardless of the dosages of LPS, the shrimp groups fed with LPS-coated pellets showed higher survival rates than the control group. There was no significant difference in survival rates between the two LPS dosages groups. In addition to survival under pathogen challenge, we also determine effect of LPS on immune-related genes after 10-day feeding trial. Gene expression analysis in the P. monodon intestines revealed that antilipopolysaccharide factor isoform 3 (ALF3), C-type lectin, and mucine-like peritrophin (mucin-like PM) were expressed significantly higher in a group fed with LPS supplemental diet once or twice a day than in a control group. The transcript levels of C-type lectin and mucin-like PM had increased significantly when LPS was given once a day, while significant induction of ALF3 transcripts was observed when shrimp were fed with LPS twice a day. The up-regulation of the immune gene levels in intestines and higher resistance to V. harveyi of the shrimp fed with LPS provide the evidence for potential application of LPS as an immunostimulant in P. monodon farming.