Transcriptional profiling of geniposide bioconversion into genipin during gardenia fructus extract fermentation by Lactobacillus (Lactiplantibacillus) plantarum SN13T

Lactiplantibacillus plantarum SN13T is a probiotic plant-derived lactic acid bacterium that can grow in various medicinal plant extracts. In this study, we fermented an aqueous extract of gardenia fructus, the fruit of a medicinal plant, with SN13T, such that the bioactivity of the extract was potentiated after fermentation to suppress the release of inflammatory mediators, such as nitric oxide (NO), reactive oxygen species (ROS), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), as well as downregulate inflammatory genes in lipopolysaccharides (LPS)-stimulated RAW 264.7 cells. This increased antioxidant and anti-inflammatory activity was mediated through bioconversion of the iridoid glycoside geniposide to its aglycone genipin via the supposed hydrolytic action of β-glucosidases harbored by SN13T. In the complete genome of SN13T, ten putative genes encoding β-glucosidases of glycosyl hydrolase (GH) family 1 organized among eight gene operons were identified. Transcriptional profiling revealed that two 6-phospho-β-glucosidase genes, pbg9 and SN13T_1925, located adjacently in the gene operon SN13T_1923, were transcribed significantly more than the remaining genes during fermentation of the gardenia extract. This suggests the role of these β-glucosidases in bioconversion of geniposide to genipin and the subsequent enhanced bioactivity of the gardenia fructus extract after fermentation with SN13T.