PHB ACCUMULATING Bacillus sp. JL47 PROTECTS Penaeus monodon POSTLARVAE AGAINST PATHOGENIC Vibrio campbellii BY ENHANCING THE INNATE IMMUNE RESPONSE  

In a previous study, the addition of the PHB accumulating isolate Bacillus sp. JL47 (capable of accumulating 54.7% PHB on cell dry weight) in the diet of Penaeus monodon postlarvae significantly improved the growth, survival and robustness of the animal during culture. In this experiment, the effects of the Bacillus sp. JL47 on the immune response of P. monodon postlarvae before and after a Vibrio challenge were investigated. Shrimp postlarvae were cultured for 15 days and were fed with Artemia franciscana nauplii enriched with Bacillus sp. JL47 at 0.5 g wet bacterial weight L^-1. Shrimp receiving the Artemia nauplii without JL47 was used as control. After 15 days of feeding, shrimps were challenged with pathogenic V. campbellii LMG 21363 at 10⁶ CFU mL^-1 by immersion. Relative expression of the prophenoloxidase (proPO), transglutaminase (TGase) and heat shock protein 70 (Hsp 70) genes of the shrimp were measured before (0 h) and after the Vibrio challenge (3, 6, 9, 12, 24 h) by quantitative real-time PCR using β-actin as reference gene. The expressions of the proPO and TGase were significantly up-regulated (P<0.01) within 12 h post challenge in shrimp receiving the Bacillus sp. JL47 when compared to the challenge and non-challenge control. Hsp70 expression showed increases at 3 and 6 h post challenge in all challenge shrimps but the increases were only significant (P<0.01) at 3 h. Interestingly, proPO and TGase genes were already significantly up-regulated in Bacillus sp. JL47-fed shrimp even before the Vibrio challenge although no up-regulation was observed in Hsp70 gene. The data suggest that the protective effect of the PHB accumulating Bacillus sp. JL47 in shrimp was due to its capacity to stimulate immune related genes of the P. monodon postlarvae such as proPO and TGase.