Isolation, Identification and Characterization of A Potential Probiotic Bacteria and its Application in Aquaculture
In the current study, Bacillus subtilis PKB1 was isolated from dried anchovies and identified using morphological and biochemical analysis followed by 16S rRNA sequencing and phylogenetic analysis. The antibacterial and anti- haemolytic properties of the bacteria were also examined. Probiotic qualities were assessed by measuring the isolated strain's tolerance to artificial gastric juice. To assess the isolated strain's capacity for stress tolerance, additional exposure to varied pH, temperature, and organic solvent concentrations was given. Bacillus subtilis in MRS medium produced exopolysaccharide (EPS) which was purified and a maximum yield of 1928mg/L was achieved. The novel exopolysaccharide was purified and characterized to be a heteropolysaccharide. The polysaccharide present had a molecular weight of about 20 kDa overall. FTIR spectroscopy revealed the presence of carboxyl, hydroxyl, and methylene groups in the EPS. The extremely cross-linked structure of the EPS with lumps that resembled spikes was revealed by atomic force microscopy. Scanning Electron Microscopy (SEM) revealed that it possessed rough, asymmetrical lumps. Emulsification activity was also observed in the EPS. The current study's findings suggested that this EPS might make a good candidate for further applications. Utilizing probiotics derived from unconventional sources may improve the variety of probiotics accessible for use in aquaculture procedures. Probiotics are used in the field of aquaculture in order to improve immunity and to protect against pathogenic microbes. Species such as Aeromonas hydrophila and Vibrio parahaemolyticus are responsible for increasing mortality, decreasing production efficiency and forcing antibiotic overuse. In this study, the role of the isolated probiotic in promoting growth performance in Nile tilapia was examined using growth and challenge studies. The experiment was conducted for a duration of 30 days. Weight gain, histology and mortality rates were studied in the presence and absence of pathogenic microbes. Bacillus subtillis PKB1 supplementation for Nile tilapia helped to maintain the integrity of gill filaments and improved survivability and weight gain when used at a concentration of 1x104 CFU/ml. The study showed that the isolate improved the survival rate of Nile Tilapia against Vibrio parahaemolyticus and Aeromonas hydrophila.