Dietary Supplementation with Recombinant Bacillus subtilis Expressing Insulin-Like Growth Factor 1a (IGF1a) Promotes Muscle Hypertrophy in Zebrafish (Danio rerio).

Aquaculture is a key sector for animal protein production that has shown significant growth, which can be further improved in terms of carcass yield and fillet quality. Enhancing skeletal muscle growth in fish through biotechnological strategies is a promising alternative with substantial commercial application potential. Fish growth regulation occurs via the somatotropic axis, where Insulin-Like Growth Factor 1 (IGF1) plays a critical role in skeletal muscle hyperplasia and hypertrophy. In this study, a strain of the probiotic bacterium Bacillus subtilis was genetically modified to express zebrafish (Danio rerio) IGF1a, which was used as a dietary supplement for zebrafish. The experiment lasted 60 days, during which zootechnical performance, muscle morphometry, and the gene expression of the IGF system, as well as muscle development genes, were evaluated. The results demonstrated that supplementation with the genetically modified probiotic improved zootechnical performance and induced muscle hypertrophy in the fish. Additionally, it promoted the induction of IGF1Rb receptor and Myf5 expression in skeletal muscle. These findings suggest that IGF1a produced and secreted by B. subtilis in the zebrafish intestine was able to trigger an endocrine action, interacting with the IGF1Rb receptor in the muscle and promoting hypertrophy. The results provide evidence of the potential of B. subtilis as a biofactory for growth factors capable of impacting the host and inducing tissue-specific growth, which could enhance carcass yield in fish used in commercial aquaculture.