Dynamics of the Intestinal Microbiota of Zebrafish Under the Influence of a Synbiotic Based on Bacillus subtilis MT74

The development of probiotic and synbiotic preparations for aquaculture is of considerable practical importance. However, research in this field has typically focused on end-point effects, whereas the dynamics of the interactions between the probiotic, the host, and the intestinal bacterial communities remain insufficiently characterized. In this study, we evaluated the effect of a synbiotic supplement based on the Bacillus subtilis MT74 strain on the composition of the gut microbiota and gene expression in zebrafish (Danio rerio). Fish received either the synbiotic supplement or equivalent dietary doses of its individual components, namely Bacillus subtilis MT74 culture and inulin. Gut microbial community composition was assessed by 16S rRNA gene amplicon sequencing, and the expression of igf1, hsp70l, gsta.1, lyz, mt2, and b2m was evaluated on days 6, 15, and 30. In addition, the persistence of the studied strain in the gut microbiota after discontinuation of its dietary administration was evaluated. The results revealed multistage changes in gut microbiota composition and host gene expression profiles. These findings indicate that microbiome restructuring and stabilization during dietary intervention are dynamic processes accompanied by changes in host regulatory responses.