Genomic and safety assessment of Niallia circulans SWUN-Y10 reveals probiotic potential

This study assessed the safety and probiotic properties of Niallia circulans SWUN-Y10, through both in vitro methods such as antibiotic susceptibility testing, biogenic amine testing, and virulence gene analysis, and in vivo methods including biochemical testing, routine blood index testing, bacterial displacement capacity, and histopathology analysis. The whole genome sequence of SWUN-Y10 was determined to be 5074781 bp in length, with an average G+C content of 35.41%, which encoded totally 5269 genes. Genomic analysis confirmed the absence of genes encoding critical virulence factors and identified only a single chromosomal antibiotic resistance gene (vmlR); alongside genes associated with carbohydrate metabolism and stress tolerance were also identified. In vitro phenotypic characteristics demonstrated the strain was also safety, evidenced by non-hemolytic activity, lack of biogenic amine production, and broad antibiotic susceptibility. Furthermore, SWUN-Y10 exhibited robust in vitro probiotic attributes, including high tolerance to simulated gastrointestinal stress (pH 2.0, 0.3% bile salts), significant auto-aggregation, and substantial cell surface hydrophobicity. The results of 14-day acute oral toxicity test showed that Niallia circulans SWUN-Y10 (10¹¹ CFU/kg body weight) did not cause significant effect on the normal growth, erythrocytes, white blood cells, and other routine blood parameters in mice. Furthermore, there was no bacteria migration observed in the liver, kidney, spleen, or heart during the feeding trial, which indicated that Niallia circulans SWUN-Y10 did not cause any infections in vivo. Moreover, H&E staining showed no evidence of lesion damage to the liver. To sum up, Niallia circulans SWUN-Y10 exhibits a promising safety and functional probiotic properties, supporting its potential use in future as a starter culture for food fermentation or as a probiotic supplement.