Dietary Administration Effects of Microbial Exopolysaccharide from <i>Bacillus subtilis</i> P1 on Growth Performance and Immunity in Nile Tilapia (<i>Oreochromis niloticus</i>)
Exopolysaccharide (EPS)-producing bacteria were isolated from the intestines of freshwater fish as prebiotics. Among the isolates, <i>Bacillus</i> sp. P1 was the potent EPS producer, with a high EPS production, and was then identified as <i>Bacillus subtilis</i> P1 based on 1...
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| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-10-01
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| Series: | Microbiology Research |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2036-7481/15/4/148 |
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| Summary: | Exopolysaccharide (EPS)-producing bacteria were isolated from the intestines of freshwater fish as prebiotics. Among the isolates, <i>Bacillus</i> sp. P1 was the potent EPS producer, with a high EPS production, and was then identified as <i>Bacillus subtilis</i> P1 based on 16S rRNA and biochemical characteristics. The produced microbial EPS was characterized by its functional groups by FTIR, showing a 90.20% correlation to inulin, while the EPS molecular weight was approximately 10<sup>5</sup> Da with a high PDI (>1.5). Moreover, the EPS from <i>B. subtilis</i> P1 was assessed for prebiotic properties by growing probiotic bacteria, and significant cell growth occurred in sugar-free TSB with 0.5% EPS (<i>p</i> < 0.05). EPS exhibited approximately 55.37% DPPH radical scavenging at 20 mg/mL and inhibited certain fish pathogens at 400 μg/mL (10–13 mm inhibition zone). Low EPS cytotoxicity was confirmed (<1% hemolysis) prior to use as immunobiotics in Nile Tilapia (<i>Oreochromis niloticus</i>) diet supplementation. Nile tilapia growth and immune response were monitored after feeding with control (C), basal diet (BD), and treatment (T): BD + EPS 5 g/kg. In the T-group, the weight gain (WG), % specific growth rate (SGR), and average daily gain (ADG) significantly increased compared to the control (<i>p</i> < 0.05) by week 4, with no negative effects on blood chemistry parameters. Lysozyme activity and respiratory burst activity in T-groups were significantly higher than the control (<i>p</i> < 0.05), with a 50% RLP survival rate of Nile Tilapia infected by <i>Aeromonas veronii</i> in the T-group after a two-week challenge. On the other hand, the proximate analysis revealed higher protein content in the T-group. These findings suggest that EPS from <i>B. subtilis</i> P1 in fish diets efficiently supports fish growth and stimulates innate immune response in Nile Tilapia, thus showing potential as the immunobiotics for aquaculture. |
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| ISSN: | 2036-7481 |