High amorphous poly-beta-hydroxybutyrate (PHB) content in a probiotic Bacillus strain displays better protective effects in Vibrio-challenged gnotobiotic Artemia

Abstract

In this study, the Bacillus sp. JL47, a superior PHB-accumulating Bacillus strain identified from the previous work, was tested for its protective effects in gnotobiotic Artemia franciscana during a pathogenic Vibrio campbellii challenge. The utilization of gnotobiotic Artemia is important in this experiment because any possible microbial interference (which are naturally present in conventional culture system) are eliminated in this model culture system, hence the interpretation of the results in this mechanistic study can be more conclusive. The survival of the Artemia fed the Bacillus sp. JL47 at 1 × 10⁷ cells mL^–1 was significantly higher as compared with the challenged control and the survival was almost doubled when the dose was increased to 5 × 10⁷ cells mL⁻¹. However, feeding the Artemia at 106 cells mL⁻¹ or lower showed no significant protective effects. Based on these densities, the estimated concentration of amorphous PHB showing a significant protection in Artemia was c. 2.44 mg L⁻¹ and the effects were even better when the amorphous PHB level was increased to 12.19 mg L⁻¹. Furthermore, feeding Bacillus sp. JL47 containing 55% amorphous PHB (on CDW) to Artemia showed a significantly higher survival in a Vibrio challenge relative to Bacillus containing 29% PHB. The data suggest that the amorphous PHB accumulated in the Bacillus sp. JL47 strain is an important determinant for the increased survival of challenged Artemia.