Probiotic, antimicrobial and anticancer properties of Lysinibacillus macroides, Kurthia huakuii, and Enterococcus faecium isolated from freshwater snail gut microbiota.

Background: The composition and roles of intestinal microbial populations have been clarified including mammals and humans however, less is understood concerning the gut microbiota of mollusks. For the first time, we investigated non-parasite transmitting freshwater snails Lanistes carinatus (L. carinatus), Cleopatra bulimoides (C. bulimoides) and Helisoma duryi (H. duryi) gut microbiota as a source of probiotic strains with anticancer potential and explore their microbial population structure.

Results: Our investigation demonstrated significant variation in microbial richness, identifying 32 bacterial phyla across the three snail species. Pseudomonadota (44-60%) and Bacteroidota (17-20%) were identified as the predominant phyla in all snails, with p value = 0.28 and 0.39, respectively in relative abundance. Distinct compositional changes were observed as L. carinatus had a greater abundance of Bacillota. H. duryi exhibited higher microbial diversity with Verrucomicrobiota and Cyanobacteria comprising 5-20% of its gut microbiota. Lysinibacillus macroides (L. macroides), Kurthia huakuii (K. huakuii) and Enterococcus faecium (E. faecium) were isolated from L. carinatus, C. bulimoides and H. duryi, respectively. L. macroides, K. huakuii and E. faecium demonstrated antimicrobial efficacy towards selected pathogenic strains. The bacterial isolates displayed significant tolerance to acidic pH and bile salts concentrations (0.3% and 0.7% w/v). The cytotoxicity of the microbial isolates secreted metabolites was examined using the MTT assay. Cytopathological changes and caspase-3 / TNF α immunohistochemistry were examined on Caco-2 cells. Results demonstrated the anticancer activity of the metabolites of the three microbial isolates on Caco2 cells where K. huakuii exhibited the highest enhancement in apoptosis and necrosis.

Conclusions: Our study identified diverse bacterial populations in freshwater snail gut microbiota with compositional differences. The isolated bacterial strains showed promising antimicrobial properties and anticancer potential, particularly K. huakuii. These results suggest that snails could be used as niche sources for beneficial bacteria with biotechnological and therapeutic applications.