Bacillus spp. isolated from intestine of Oreochromis mossambicus: Identifying a potential probiotic for tilapia culture

Abstract

Aquaculture industries are currently facing a wide array of challenges including emergence of antimicrobial resistance among pathogens, increased susceptibility to diseases, lack of healthy fingerlings and overall decrease in productivity. Probiotics are safer alternatives to antimicrobials and serves as a solution all these concerns. Oreochromis mossambicus is a commercially significant fish species of the cichlid family due to its richness in micro and macronutrients, adaptability and feed efficacy. Management of pathogenic infections and availability of healthy fingerlings are two major challenges faced by the tilapia farmers at present. The current research was conducted to identify a potent bacterial strain from the intestine of O. mossambicus with active probiotic properties. A potent Bacillus strain that surpassed the safety assessments and exhibited antagonistic activity against the potential aquaculture pathogens, Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pyogenes were selected for determination of specific probiotic properties. The strain was found tolerant to 0.3% bile, acidity up to pH 2 and 5% NaCl concentrations, substantiating its potential to survive the hostile gut environment of the host fish. Additionally, the strain exhibited auto aggregation and cell surface hydrophobicity, which are essential probiotic properties. It showed 63±3.32%. hydrophobicity and 56.65±1.65% auto aggregation in spectrophotometric studies. Moreover, it also demonstrated proteolytic activity that could benefit the host in the digestion processes. As the strain exhibited desirable probiotic traits, it was subjected to molecular characterization and identified as Bacillus tropicus ACS1. Further research is warranted to elucidate its complete potential in promoting the health, immunity and productivity of aquaculture industries.