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. 2024 Feb 14;14(1):3720.
doi: 10.1038/s41598-024-54380-7.

Probiotic performance of B. subtilis MS. 45 improves aquaculture of rainbow trout Oncorhynchus mykiss during acute hypoxia stress

Alireza Neissi  1 , Hamed Majidi Zahed  2 , Reza Roshan  2
Affiliations

Probiotic performance of B. subtilis MS. 45 improves aquaculture of rainbow trout Oncorhynchus mykiss during acute hypoxia stress

Alireza Neissi et al. Sci Rep. .

Abstract

The aim of this study was to produce mutant strains of Bacillus subtilis with high probiotic performance for use in the aquaculture of rainbow trout Oncorhynchus mykiss. The main strain of B. subtilis (MS) was irradiated with gamma rays (5.3 KGy). Subsequently, the B. subtilis mutant strain no. 45 (MS. 45) was selected for bacterial growth performance, resistance to acidic conditions, resistance to bile salts and antibacterial activity against Aeromonas hydrophila and Pseudomonas fluorescens. After 60 days, the rainbow trout (70.25 ± 3.89 g) fed with MS. 45 and MS were exposed to hypoxia stress (dissolved oxygen = 2 ppm). Subsequently, immune indices (lysozyme, bacterial activity and complement activity), hematological indices [hematocrit, hemoglobin, WBC, RBC, mean corpuscular volume (MCV)] and antioxidant factors (T-AOC, SOD and MDA)) were analyzed after and before hypoxia exposure. The expression of immunological genes (IFN-γ, TNF-α, IL-1β, IL-8) in the intestine and the expression of hypoxia-related genes (HIF-1α, HIF-2α, FIH1) in the liver were compared between the different groups under hypoxia and normoxia conditions. Growth, immunological and antioxidant indices improved in group MS. 45 compared to the other groups. Stress indices and associated immunologic and hypoxia expressions under hypoxia and normoxia conditions improved in MS. 45 compared to the other groups. This resulted in improved growth, immunity and stress responses in fish fed with the microbial supplement of MS. 45 (P < 0.05) under hypoxia and normoxia conditions, (P < 0.05), resulting in a significant improvement in trout aquaculture.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Survival of B. subtilis during irradiation with doses of 1, 2, 3, 4 and 5 kGy. (b) Growth rate of the mutant strains and the main strain of B. subtilis for 20 h.
Figure 2
Figure 2
Average survival percentage of mutant and non-mutant strains of B. subtilis with 0.3% bile salt within 4 h.
Figure 3
Figure 3
Antagonistic activities of B. subtilis mutant strains (11, 12, 31, 32) and the main strain (MS, 21, 22) against A. hydrophila and P. fluorescens by diffusion method in agar troughs.
Figure 4
Figure 4
Comparison (mean ± SD) of initial weight (a), specific growth rate (b), weight gain (c) and feed conversion ratio (FCR) (d) in rainbow trout fed the B. subtilis main strain (MS), the mutant strain (MS. 45) and C (without microbial supplement) after 8 weeks of feeding (P < 0.05).
Figure 5
Figure 5
Comparison (mean ± SD) of (a) complete blood count (CBC), neutrophil lymphocytes, monocytes, eosinophils; and (b) immunological performance; bacterial activity, lysozyme, C3 activity, in rainbow trout sera treated with B. subtilis main strain (MS), B. subtilis Mutant strain number 45 (MS. 45) and control (no microbial supplementation) after 8 weeks feeding (P < 0.05).
Figure 6
Figure 6
(a) comparison (mean ± SD) of glucose and (b) cortisol in sera of rainbow trout treated with B. subtilis main strain (MS), MS. 45 (B. subtilis No. 45) and the control (no microbial supplementation) after 8 weeks (P < 0.05).
Figure 7
Figure 7
Comparison (mean ± SD) of antioxidant factors (a). T-AOC, (b) SOD and (c) MDA in rainbow trout treated with B. subtilis main strain (MS), B. subtilis No. 45 (MS. 45) and control (no microbial supplementation) after 8 weeks feeding (P < 0.05).
Figure 8
Figure 8
Comparison (mean ± SD) of the expression of (a). immunological genes (IFN-γ, TNF-α, IL-1β, IL-8) in the intestine and the expression of (b) hypoxia- related genes (HIF-1α, HIF-2α, FIH1) in the liver of rainbow trout fed with the B. subtilis main strain (MS) and mutant No. 45 (MS. 45) after 8 weeks under hypoxia and normoxia conditions. MS (main strain), control (no microbial supplementation), and No. 45 (B. subtilis No. 45) (P < 0.05).
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