Dietary gold nanoparticles modulate the gut microbiota of Mystus vittatus (Bagridae): evidence from 16S rRNA amplicon sequencing

We evaluated whether biosynthesized gold nanoparticles (AuNPs) used as a dietary supplement reshape the gut microbiota of Mystus vittatus using 16S rRNA (V3-V4) amplicon sequencing. Across all samples, we resolved 716 amplicon sequence variants (ASVs) spanning 20 phyla, 33 classes, 75 orders, 129 families, and 190 genera. AuNP-fed fish showed numerically higher richness and evenness than controls; however, alpha-diversity indices (Chao1, Shannon, and Simpson) and beta-diversity (unweighted UniFrac PCoA) did not differ significantly (P>0.05). Despite the lack of whole-community separation, several taxa responded to AuNPs. Genera detected as candidate biomarkers in univariate testing included Ralstonia, Rikenellaceae_RC9_gut_group, Candidatus Arthromitus, Family_XIII_AD3011_group, and Undibacterium, alongside a higher relative abundance of Bacillus—consistent with putative probiotic activity reported in fish. Community-function predictions with PICRUSt2 indicated enrichment of pathways related to amino acid and energy metabolism, nucleotide metabolism, and replication/repair in the AuNP group, whereas carbohydrate-focused pathways (for example, glycolysis and fructose/mannose metabolism) were relatively higher in controls. These results suggest that dietary AuNPs can shift microbiome composition and predicted functional potential toward profiles compatible with improved nutrient processing and immune readiness. Because functional inferences were derived from 16S marker data rather than shotgun metagenomes, they should be interpreted cautiously. We also note that community-level diversity differences represented trends rather than statistical separations. Overall, AuNP supplementation at 50 mg/kg produced measurable changes in the microbiome without disrupting the core phylum-level structure. These findings support further evaluation of AuNPs as a feed additive in aquaculture, including dose–response testing, validation using metagenomic or metatranscriptomic sequencing, and long-term safety assessments that track performance, disease outcomes, and environmental release.