Effects of host gut-derived probiotic bacteria on gut morphology, microbiota composition and volatile short chain fatty acids production of Malaysian Mahseer Tor tambroides

Three host-associated probiotics (Bacillus sp. AHG22, Alcaligenes sp. AFG22, and Shewanella sp. AFG21) were isolated from the gastrointestinal tract of Tor tambroides, and their effects were evaluated on gut morphology, microbiota composition and volatile short chain fatty acids (VSCFAs) production of the same species. A control diet (40% crude protein and 10% lipid) was formulated, and three different probiotic supplemented diets were prepared by immersing the control diet in each host-derived isolated probiotic, suspended in sterile phosphate buffered saline (PBS), to achieve concentration at 1.0 × 108 CFU g−1 feed. Triplicate groups of T. tambroides juveniles (1.39 ± 0.06 g) were stocked in twelve glass aquaria (100 L capacity) with stocking density of 20 individuals per aquarium. The feed was applied twice daily at 3.0% of the body weight per day for 90 days. The intake of probiotics drastically modified the gut microbiota composition. The average number of OTUs, Shannon index and Margalef species richness were significantly higher in host-associated probiotic treatments compared to the control. A significant increase of lipolytic, proteolytic and cellulolytic bacterial number were observed in the gastrointestinal tracts of T. tambroides fed the diets supplemented with Alcaligenes sp. AFG22 compared to the control. Villus length, villus width and villus area were significantly higher in T. tambroides juveniles fed the diet supplemented with Alcaligenes sp. AFG22. Acetate and butyrate were detected as main VSCFA production in the gastrointestinal tract of T. tambroides. Acetate and total VSCFAs production in Alcaligenes sp. AFG22 supplemented treatment was significantly higher than control. These results indicate that host-derived probiotics, especially Alcaligenes sp. has a significant potential as an important probiotic to enhance the nutrients utilization and metabolism through increasing gut surface area and VSCFAs production, and adjusting gut microbiota balance of T. tambroides juveniles