Characterization of a Bacillus sp. KRF-7 isolated from the intestine of rockfish and effects of dietary supplementation with mannan oligosaccharide in rockfish aquaculture. Issue 119 (December 2021) - Jang, Won Je
Abstract: The purpose of this study was to characterize the bacteria isolated from rockfish intestines and to investigate the effects of feed supplementation in rockfish aquaculture. Bacillus sp. KRF-7 isolated from the intestine of rockfish ( Sebastes schlegelii ) was demonstrated to be safe based on in vitro tests confirming the absence of hemolysis, cytotoxicity, and genes with toxigenic potential. In a feeding trial, providing a supplemental diet of 1 × 10 8 CFU g −1 Bacillus sp. KRF-7 was observed to positively alter the weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio of juvenile rockfish. KRF-7 supplementation showed positive regulation of nonspecific immune parameters, such as superoxide dismutase, lysozyme activity, and myeloperoxidase activity. This analysis also revealed a change in the composition of the intestinal microbiota at the phylum level from Proteobacteria to Firmicutes. In both the kidney and spleen, the expression levels of IL-10, NF-κB, and B cell activating factors in the KRF-7-supplemented group were significantly increased compared to those in the control group. Therefore, this study verified the safety of KRF-7 isolated from the intestine of rockfish and suggests that dietary supplementation with KRF-7 enhances the growth performance of rockfish and has beneficial effects on the regulation of the intestinal microbiota and immune response. Highlights: The probiotic properties of Bacillus sp. KRF-7 were investigated. Dietary supplementation of KRF-7 upregulated the growth performance of rockfish. Supplementation with KRF-7 modulated gut microbial community of rockfish.