Dietary probiotic Bacillus OJ and isomaltooligosaccharides influence the intestine microbial populations, immune responses and resistance to white spot syndrome virus in shrimp (Litopenaeus vannamei)
Introduction
Increasing with the demand for environment friendly aquaculture, probiotics or prebiotics, used as immunostimulants, have received heightened attention. A probiotic is, by definition, ‘a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance’ (Fuller, 1989). However in aquaculture, probiotic can be administered either as a food supplement or as an additive to the water (Moriarty, 1998). In recent years, there were increasing researches have demonstrated that probiotics can enhance the disease resistance of shrimp / fish by suppressing the pathogens, enhancing immunity or improving water quality (Verschuere et al., 2000). Thus, usage of probiotics has been considered as one of the most promising preventive methods in aquaculture. Quite a few microorganisms from the genus Bacillus have been used widely as putative probiotics. Correspondingly, their nutritional and healthy benefits have also been demonstrated in shrimp (Rengpipat et al., 1998, Rengpipat et al., 2000, Sugita et al., 1998).
In an analogy with probiotics, prebiotics were classified as “nondigestible food ingredients that beneficially affect the host by stimulating growth and/or activity of a limited number of bacteria in the intestine” (Delzenne and Roberfroid, 1994). Although the nutritional and healthy benefits have also been demonstrated for some oligosaccharides on fish (Glencross et al., 2003, Li and Gatlin, 2005, Pryor et al., 2003, Welker et al., 2007), the development that has been made in prebiotics for acquittal animal is more primitive than for poultry. Isomaltooligosaccharides (IMO) are a mixture of isomaltose, isomaltotriose, panose, isomaltotetraose, etc. On poultry, numerous research efforts have confirmed the significant efficacy of IMO as prebiotics (Chung and Day, 2004, Thitaram et al., 2005, Zhang et al., 2003). To the best of our knowledge, in contrast to fish / poultry studies, there is scarcely any research on the prebiotic effects of oligosaccharides (including isomaltooligosaccharides) in shrimp and other crustaceans.
Generally, probiotics and prebiotics are mostly investigated separately. The synbiotics, as a combination of probiotics and prebiotics, have not been intensively studied to date. Their individual advantages might be additive or even synergistic but this hypothesis needs to be qualified.
Therefore, this study aimed to evaluate the potential of bacterium Bacillus OJ, a potential probiotic strain isolated from the Pacific white shrimp (Litopenaeus vannamei), as the dietary probiotics, as well as the synergistic effects of PB and IMO on the intestine microbial populations, immune responses and disease resistance of shrimp (Litopenaeus vannamei).
Section snippets
Bacteria and isomaltooligosaccharides
The bacterial strain used in this study, bacterium OJ, was previously isolated from the digestive tracts of Pacific white shrimp (Litopenaeus vannamei), in Qingdao, China. Based on the morphological, physiological and biochemical characteristics described in the Bergey's Manual of Systematic Bacteriology (Holt et al., 1994), the bacterial strain OJ was identified. Probiotic bacteria were cultured in liquid media for marine bacteria (2216E) with a shaking incubator at 200 rpm for 24 h at 27 C.
Identification of the bacterium OJ
Based on the morphological, physiological and biochemical characteristics, the strain OJ identified as Bacillus megeterium since displaying the same phenotype with standard bacterium strain (Table 1).
Survival of shrimp
Shrimp survivals significantly increased with the increasing doses of dietary PB in diet (One-way ANOVA, P < 0.05; Fig. 1). During the whole experimental period, shrimp fed with the control diet produced the lowest survival, and were significantly different (One-way ANOVA, P < 0.05) from the groups fed
Discussion
In this present study, based on the morphological, physiological and biochemical characteristics, the strain OJ identified as Bacillus megeterium. Although diet containing 0.2% isomaltooligosaccharides (IMO) excreted no significant protection on the shrimp from the white spot syndrome virus (WSSV), either certain dose of PB alone or in combination with 0.2% IMO can significantly reduce mortality of the shrimp challenged by WSSV, modulate the intestinal microflora, as well as stimulate immunity
Acknowledgment
This work was financially supported by the National High Technology Research and Development Project of China (863 Project, No. 2001AA622060 and 2003AA622060).
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