Gut bacterial community structure and functional analysis in the silkworm Samia ricini reared on the secondary food plant Tapioca (Manihot esculenta Crantz)

In the present study, the bacterial diversity in the gut of Eri silkworm (Samia ricini) fed with tapioca leaves was assessed using a culture-independent metagenomics approach. Additionally, the study aimed to predict the functional roles of gut bacterial communities by analysing gene involvement in various KEGG pathways. A total of 564 operational taxonomic units (OTUs) were identified, with Proteobacteria (69.15%), Firmicutes (28.37%) and Actinobacteria (1.77%) being the dominant phyla. Gammaproteobacteria was the most abundant class while Enterobacterales emerged as the dominant order, with Enterobacteriaceae being the most prevalent family. Co-occurrence analysis revealed nine bacterial genera: Lactobacillus, Enterococcus, Lactococcus, Enterobacter, Bacillus, Stenotrophomonas, Staphylococcus, Serratia and Klebsiella, suggesting similar habitat or nutritional niche preferences. This study represents the report on gut bacterial populations in S. ricini larvae fed on tapioca leaves, a key secondary food widely adopted by rearers. PICRUSt2 analysis revealed diverse gene functions across KEGG pathways, particularly in membrane transport, carbohydrate metabolism, amino acid, lipid and nucleotide metabolism, cellular processing and signalling, gene expression and xenobiotic degradation, highlighting their roles in host physiology. These findings provide valuable insights into Eri silkworm gut microbiota, with dominant bacterial taxa having potential applications in probiotic development and biotechnological metabolite production.