Characterization, screening, and application of bacteria with probiotic properties isolated from the gut of Labeo calbasu (Hamilton)
Labeo calbasu is not reared in aquaculture because of the unavailability of proper feed and the risk of infection. The ability of probiotics to promote growth and immunological defense barriers in the gut has led to the use of autochthonous probiotic bacteria. Hence, the present study was conducted to screen potential probiotic bacteria from the gut of L. calbasu and to supplement the same to study the effect on growth and immunity. Strains with probiotic properties were assayed for exogenous enzyme production and identified based on phylogenetic analysis and nucleotide homology. Four of nine isolates showed promising antibacterial activity against Aeromonas hydrophila. The strains survived in relatively low pH and high bile concentrations and were investigated for hydrophobicity, autoaggregation, and coaggregation. Based on the positive results of this study, the LC1 and LC4 strains (analysed with 16S rRNA gene sequencing and showing similarity with Aneurinibacillus aneurinilyticus and Stenotrophomonas sp.) were further incorporated into diets to explore their probiotic effects on the growth performance and immunity of the fish. Administering the probiotics elevated growth parameters and benefitted the immune system by increasing the phagocytic index and decreasing the mortality rate with exposure to A. hydrophila.