Enhancement of growth, intestinal microbiota, and innate immune protection against Vibrio alginolyticus in white shrimp (Penaeus vannamei) following dietary administration with Bacillus safensis NPUST1.

Abstract

Spore-forming Bacillus probiotics have attracted increasing interest as antibiotic-free functional feed additives in shrimp aquaculture. However, evidence for the probiotic potential of Bacillus safensis remains limited. This study evaluated the effects of dietary B. safensis NPUST1 on growth performance, innate immunity, intestinal microbiota, and resistance to Vibrio alginolyticus in white shrimp (Penaeus vannamei). Shrimp were fed a basal diet (control) or diets supplemented with NPUST1 at 105 (E-5), 106 (E-6), or 107 CFU g-1 (E-7) for 8 weeks. Disc diffusion assays showed measurable inhibition zones against all antibiotics tested. Compared with the control, the E-6 and E-7 diets significantly increased final body weight, weight gain, specific growth rate, and feed efficiency without affecting survival. Probiotic supplementation also enhanced innate immunity, as indicated by increased phenoloxidase activity in the E-6 and E-7 groups, elevated phagocytic activity in all probiotic-treated groups, and higher respiratory burst, superoxide dismutase, and lysozyme activities, particularly in the E-7 group. Expression of prophenoloxidase was upregulated in the E-6 and E-7 groups, whereas TNF-α and astakine were significantly upregulated in all probiotic-treated groups. Following V. alginolyticus challenge, NPUST1 supplementation reduced cumulative mortality in a dose-dependent manner. Intestinal microbiota analysis revealed distinct diet-associated shifts in community composition, characterized by reduced Vibrio, Flavobacterium, and Tenacibaculum abundance together with enrichment of beneficial genera, including Bacillus and Bifidobacterium. Overall, dietary supplementation with B. safensis NPUST1 was associated with improved growth performance, enhanced innate immune responses, reduced mortality following V. alginolyticus challenge, and changes in intestinal microbial composition. The 107 CFU g-1 diet showed the most consistent overall effects, supporting its potential application in white shrimp culture.