Vitamin B2, also known as riboflavin, is essential for maintaining human health. The purpose of this study was to isolate novel lactic acid bacteria that overproduce vitamin B2 and to validate their potential as probiotics. In this study, Lactobacillus plantarum HY7715 (HY7715) was selected among lactic acid bacteria isolated from Kimchi. HY7715 showed a very high riboflavin-producing ability compared to the control strain due to the high expression of ribA, ribB, ribC, ribH, and ribG genes. HY7715 produced 34.5 ± 2.41 mg/L of riboflavin for 24 h without consuming riboflavin in the medium under optimal growth conditions. It was able to produce riboflavin in an in vitro model of the intestinal environment. In addition, when riboflavin deficiency was induced in mice through nutritional restriction, higher levels of riboflavin were detected in plasma and urine in the HY7715 administration group than in the control group. HY7715 showed high survival rate in simulated gastrointestinal conditions and had antibiotic resistance below the cutoff MIC value suggested by the European Food Safety Authority; moreover, it did not cause hemolysis. In conclusion, HY7715 could be considered a beneficial probiotic strain for human and animal applications, suggesting that it could be a new alternative to address riboflavin deficiency.

Probiotics should be well established in the gut, passing through the digestive tract with a high degree of viability, and produce metabolites that improve the gut environment by interacting with the gut microbiome. Our previous study revealed that the Lactiplantibacillus plantarum HY7715 strain shows good bile acid resistance and a riboflavin production capacity. To confirm the interaction between HY7715 and gut microbiome, we performed a metabolite and microbiome study using a simulated gut system (SGS) that mimics the intestinal environment. Changes in the microbiome were confirmed and compared with L. plantarum NCDO1752 as the control. After 14 days, the HY7715 treatment group showed a relatively high butyrate content compared to the control group, which showed increased acetate and propionate concentrations. Moreover, the riboflavin content was higher in the HY7715 treatment group, whereas the NCDO1752 treatment group produced only small amounts of riboflavin during the treatment period and showed a tendency to decrease during the washout stage; however, the HY7715 group produced riboflavin continuously in the ascending colon during the washout period. A correlation analysis of the genus that increased as the content of riboflavin increased revealed butyrate-producing microorganisms, such as Blautia and Flavonifractor. In conclusion, treatment with L. plantarum HY7715 induced the production and maintenance of riboflavin and the enrichment of the intestinal microbiome

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