Effects of probiotic treatment on the intestinal microbial community of Haliotis diversicolor.

Probiotic treatment is an effective method for enhancing growth performance and improving intestinal flora in aquaculture species. This study examined the effects of three candidate-probiotics (Bacillus, photosynthetic bacteria, and Lactobacillus) on the rate of weight gain and the intestinal flora of abalone juveniles. Haliotis diversicolor was fed a probiotic-supplemented diet for 30 days. The abalones fed with Lactobacillus showed a more significant weight gain rate than those in the Bacillus, photosynthetic bacteria, and control groups. Through 16S rRNA high-throughput sequencing, 12,490 amplicon sequence variants (ASVs) were obtained from the abalone intestinal tract microbiome. After a short feeding period (5 days), the Bacillus and photosynthetic bacteria-treated groups showed an increased abundance of Proteobacteria in the abalone digestive tract. In the Lactobacillus-treated group, the quantity of Proteobacteria decreased, and the abundance of Bacteroidota increased. After 30 days of feeding, the abundance of Proteobacteria and Bacteroidetes at the phylum level was more significant in the Bacillus-treated group and photosynthetic bacteria-treated group than in the controls. The Lactobacillus-treated group showed an increase in the quantity of Proteobacteria and Chloroflexi. The dominant flora of the three probiotic treated groups changed slightly with respect to the control group. After a short period of feeding (5 days), the abundance of Rhodobacteraceae (at the genus level) in the abalone digestive tract increased in the Bacillus- and photosynthetic bacteria-treated groups, whereas in the Lactobacillus-treated group, Rhodobacteraceae decreased, and Maribacter increased in abundance. After 30 days of feeding, Bacteroidetes and Ruegeria were higher in the Bacillus-treated group than in the control group. Marinirhabdus and Bacteroidetes increased in the photosynthetic bacteria-treated group, and Roseivivax and Ruegeria increased in the Lactobacillus-treated group. The three probiotic-treated groups had higher microbial diversity than the control group. Therefore, our findings confirmed that adding Bacillus, photosynthetic bacteria, and Lactobacillus to the abalone diet increased abalones' weight gain rate and altered their intestinal microbiome composition.