Genomic and phenotypic-based safety assessment and probiotic properties of Streptococcus thermophilus FUA329, a urolithin A-producing bacterium of human milk origin

Abstract

Streptococcus thermophilus FUA329, a urolithin A-producing bacterium, is isolated from human breast milk. The complete genome sequence of FUA329 did not contain any plasmids and at least 20 proteins were related to extreme environment resistance. Phenotypic assay results demonstrated that FUA329 was susceptible to 12 kinds of antibiotics and did not exhibit any hemolytic or nitrate reductase activity. Three free radical scavenging assays revealed that FUA329 have high antioxidant capability. FUA329 exhibited a cell surface hydrophobicity of 52.58 ± 1.17% and an auto-aggregation rate of 18.69 ± 2.48%. Moreover, FUA329 demonstrated a survival rate of over 60% in strong acid and bile salt environments, indicating that FUA329 may be stable colonization in the gastrointestinal tract. Additionally, we firstly found 3 potential proteins and 11 potential genes of transforming ellagic acid to urolithins in FUA329 genome. The above results indicate that FUA329 has credible safety and probiotic properties, as well as the potential to be developed as a new generation of urolithin A-producing probiotics.