Hong-Ling Yang

Probiotic applications of two dominant gut Bacillus strains with antagonistic activity improved the growth performance and immune responses of grouper Epinephelus coioides

The effect of dietary administration of Bacillus pumilus and Bacillus clausii, the dominant bacteria with antagonistic activity in the gut of fast growing fish, on the growth performance and immune responses of grouper Epinephelus coioides were assessed. The fish were fed for 60 days with three different diets: control (without probiotics), diet T1 supplemented with 1.0x10(8) cells g(-1) B. pumilus, diet T2 with 1.0x10(8) cells g(-1) B. clausii. No significant improvements of weight gain or specific growth rate were observed in the probiotic fed groups, but a significant improvement of feed conversion ratio was observed after 60 days of feeding. Phagocytic activity and phagocytic index of fish fed probiotic diets were significantly higher than those of fish fed the control diet for 60 days. Superoxide dismutase (SOD) concentrations showed no significant difference between the treatments and the control during the whole experiment period, but which increased by 11.4% and 18.5% after 60 days of fed with diets T1 and T2, respectively. The serum lysozyme activities of fish fed diets T1 and T2 were significantly higher than that of fish fed control diet, and had respectively increased by 34.7% and 17.4% compared to the control after 60 days of feeding. Serum complement C3 levels of the treatments were significantly higher than that of control after 30 days of feeding, but no significant difference in serum complement C3 and C4 levels were observed between the treatments and the control after 60 days of feeding. The serum IgM levels of fish fed diet T1 and diet T2 were higher than that of fish fed control diet, and significant increase was observed in fish fed diet T2 for 30 days. The results demonstrated potential for B. pumilus and B. clausii to improve growth performance and immune responses of E. coioides.

Molecular analysis of autochthonous microbiota along the digestive tract of juvenile grouper Epinephelus coioides following probiotic Bacillus pumilus administration

Aims:  To evaluate the diversity of dominant autochthonous microbiota along the digestive tract of juvenile Epinephelus coioides following the dietary administration of probiotic Bacillus pumilus for 60 days.

Probiotic Bacillus pumilus SE5 shapes the intestinal microbiota and mucosal immunity in grouper Epinephelus coioides

The health benefits of probiotics are thought to occur, at least in part, through an improved intestinal microbial balance in fish, although the molecular mechanisms whereby probiotics modulate the intestinal microbiota by means of activation of mucosal immunity are rarely explored. In this study, the effects of viable and heat-inactivated probiotic Bacillus pumilus SE5 on the intestinal dominant microbial community and mucosal immune gene expression were evaluated. The fish were fed for 60 d with 3 different diets: control (without probiotic), and diets T1 and T2 supplemented with 1.0 × 10⁸ cells g⁻¹ viable and heat-inactivated B. pumilus SE5, respectively. Upregulated expression of TLR1, TLR2 and IL-8, but not MyD88 was observed in fish fed the viable probiotic, while elevated expression of TLR2, IL-8 and TGF-β1, but not MyD88 was observed in fish fed the heat-inactivated B. pumilus SE5. The induced activation of intestinal mucosal immunity, especially the enhanced expression of antibacterial epinecidin-1, was consistent with the microbial data showing that several potentially pathogenic bacterial species such as Psychroserpens burtonensis and Pantoea agglomerans were suppressed by both the viable and heat-inactivated probiotic B. pumilus SE5. These results lay the foundation for future studies on the molecular interactions between probiotics, intestinal microbiota and mucosal immunity in fish.

Probiotic Psychrobacter sp. improved the autochthonous microbial diversity along the gastrointestinal tract of grouper Epinephelus coioides

The effect of dietary administration of probiotic Psychrobacter sp. SE6 for 60 days on the autochthonous microbiota in the foregut, midgut and hindgut of juvenile grouper Epinephelus coioides was assessed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). A complex and generally similar bacterial composition was present along the gastrointestinal (GI) tract of fish fed the probiotic or control diet. However, samples collected from the probiotic group and control group showed different DGGE patterns. The similarity dendrogram demonstrated that all nine samples from the control group were closely related and distinctly different to the probiotic samples. The total number of bands and Shannon index of the foregut, midgut and hindgut samples in the probiotic group were significantly higher than those in the control group, suggesting probiotic Psychrobacter sp. improved the autochthonous microbial diversity along the GI tract of E. coioides. Some potentially beneficial and uncultured bacteria were stimulated, while some potentially harmful species, such as Staphylococcus saprophyticus, were suppressed. Sequence analysis showed that the majority of bacterial sequences (48.0%) in this study were highly similar to unidentified clones, suggesting a considerable proportion of unknown bacteria in the gut of E. coioides.