Effects of Bacillus subtilis BSXE-2102 in Different Forms on the Growth Performance, Non-Specific Immunity, and Disease Resistance of Litopenaeus vannamei

Bacillus subtilis is one of the most commonly used probiotics in aquaculture, but there are limited studies on the optimal forms of addition form and the differences in effects of B. subtilis in feed. In this study, we evaluated the growth, immunity and disease resistance of Litopenaeus vannamei fed diets supplemented with different forms of B. subtilis BSXE-2102, including live cells (WB), heat-killed whole cells (WK), fermentation broth (WL), fermentation supernatant (WM) and sonication-killed cell-free extracts (WN) at a concentration of 1×10¹¹ CFU/kg, five replicates each treatment, 42-day cultivation. Commercial feed was used as the control (DZ). The results showed that the survival rate each diet ranged from 85.33% to 94.67%, with WB showed the highest survival rate, significantly higher than that of WL and DZ (P < 0.05). The minced shrimp body weight and specific growth rate of WN were significantly higher than those of DZ (P < 0.05), and feed efficiency and digestibility were also significantly higher in WB, WK and WN groups compared to DZ (P < 0.05). The T-NOS and SOD activities in the serum of shrimp from all treatment groups were significantly higher than those of DZ (P < 0.05), but other antioxidant indicators varied across treatments. WB demonstrated significantly higher POD, LZM activity and PO content than DZ (P < 0.05), with the highest LZM activity recorded. WK had significantly higher ACP activity and T-AOC than DZ (P < 0.05). WL, WM and WN had significantly higher AKP, ACP, POD activity, PO content and T-AOC than DZ (P < 0.05), with the WN group showing significantly higher T-NOS activity and T-AOC than the others (P < 0.05). Compared to DZ, the expression levels of genes SOD, Relish, Toll, Imd, TOR, eIF4E1α and eIF4E2 in the hepatopancreas of shrimp in all treatment groups were significantly upregulated (P < 0.05). Among these, WN had the highest expression levels of SOD, Toll, TOR and eIF4E2 while WB had significantly higher expression of LZM and LGBP than others (P < 0.05). The challenge test of Vibrio parahaemolyticus revealed that the cumulative mortality of WN was significantly lower than that of DZ (P < 0.05). Our findings suggested that adding B. subtilis BSXE-2102 live cells and sonication-killed cell-free extracts to L. vannamei feed can significantly improve its growth performance, immunity and disease resistance. Sonication-killed cell-free extracts may serve as a potential postbiotic to enhance the growth performance, immunity and disease resistance of L. vannamei.