Impact of probiotic strain Bacillus sp. strain FM2 on Rohu (Labeo rohita) gut microbiome Metagenome
A spore-forming probiotic strain, Bacillus sp. FM2, was isolated from a fish market near Santiniketan, West Bengal, India. After comprehensive morphological, biochemical, and molecular characterization, the strain was evaluated for its ability to modulate the gut microbiota of Rohu (Labeo rohita). Experimental fish were divided into two groups: a control group (Con) fed with a basal diet, and a probiotic-treated group (Pro) fed with the basal diet supplemented with spores of Bacillus sp. FM2. The feeding trial was conducted over a period of 60 days under controlled aquaculture conditions.At the end of the feeding period, gut from randomly selected fish in each group were aseptically dissected and pooled to generate representative samples. Following this, all remaining fish were challenged with Aeromonas hydrophila (MTCC 1739), and mortality was monitored over the next 10 days. After the challenge period, gut samples were again collected from the surviving fish in each group and pooled together separately for each group (A_Con for Aeromonas challenged control group and A_Pro for Aeromonas challenged probiotic treatment group).Metagenomic DNA from all pooled gut samples (pre- and post-challenge for both control and probiotic groups) were extracted using a standard SPINeasy DNA Kit for Faeces/Soil (MP Biomedicals, Santa Ana, CA). Employing the metagenomic DNA samples, the V1-V2 hyper-variable region of the 16S rRNA gene was amplified using region-specific universal primers. Amplicon libraries were prepared and sequenced on the Ion Torrent platform to assess the taxonomic composition and diversity of the gut microbiota in response to probiotic treatment and pathogen challenge.