Evaluating the Probiotic Potential of Lactic Acid Bacteria Isolated from Nipponia nippon Feces

This study aims to identify an optimal lactic acid bacterial strain from the feces of healthy Nipponia nippon . From the fecal samples, twenty isolates were obtained. The isolates were subjected to biochemical identification, acid and bile tolerance tests, in vitro inhibition of pathogenic bacteria assays, cell surface hydrophobicity assessment, antibiotic susceptibility test, and hemolytic activity evaluation to determine their probiotic potential. The results indicated that six isolates (D1, D2, D6, E7, D8, D9) could survive in low acid and high bile salt conditions. Except for D8, all six isolates exhibited inhibitory activity against tested pathogens. Isolates D6 and E7 showed the least resistance to antibiotics, and only E7 demonstrated moderate hydrophobicity. The E7 strain was further studied in depth and identified as L. plantarum through 16srRNA sequencing. To assess its safety, mice were fed with the E7 strain, and the results showed no deaths or adverse effects on blood cellular components. Whole genome sequencing of Lactobacillus plantarum E7 using Nanopore PromrthION48 and the Illumina Novaseq revealed a ring chromosome and two ring plasmids. The chromosome encodes 3024 genes, some associated with cell adhesion, acid and bile salt tolerance, antioxidant enzymes, and secondary metabolites. Plasmids contained fewer coding genes. The VFDB database detected only a few virulence genes related to adherence, stress survival, exoenzyme production, immune modulation, and regulation factors. KEGG database analysis indicated that the genes of this bacterium are primarily involved in carbohydrate metabolism, amino acid metabolism, vitamin and cofactor metabolism, environmental information processing and genetic processing. This study lays a theoretical foundation for the clinical application and development of probiotics.