Gut Bacterium Unmasked as Powerful Transformer of Licorice Compound

Licorice root has been chewed, brewed, and prescribed for thousands of years, from the pharmacies of Traditional Chinese Medicine to Ayurvedic formulations and European herbal remedies. Its sweet extract is now found everywhere from candies and herbal teas to beverages, and much of its celebrated bioactivity has been attributed to a chalcone-type flavonoid called licochalcone A. This molecule, built from two aromatic rings joined by an α,β-unsaturated carbonyl system and decorated with hydroxyl and prenyl groups, has been credited with antitumor, anti-inflammatory, cardioprotective, and antioxidant effects, and animal studies suggest it can improve glucose homeostasis, lipid metabolism, and even inflammatory bowel conditions. Yet a fundamental question has lingered: what actually happens to licochalcone A once it reaches the trillions of microbes colonizing the human gut? A new study published in the Journal of Agriculture and Food Research offers the most detailed answer yet, and the identity of the microorganism doing much of the work is a genuine surprise.

Researchers at Huazhong Agricultural University began by asking whether the human gut microbiota as a whole could degrade licochalcone A. They recruited four healthy young Chinese men aged 24 to 27, excluding anyone with recent antibiotic use, probiotic consumption, gastrointestinal disorders, or metabolic disease, and collected fresh fecal samples that were processed entirely inside an anaerobic chamber to preserve the viability of oxygen-sensitive microbes. Each donor’s microbiota was then cultured in broth supplemented with licochalcone A and monitored for 48 hours. The results revealed striking interindividual variability: the most efficient community, from Donor A, degraded roughly 55 percent of the compound, while the least efficient, from Donor C, managed only about 27 percent. This spread matters, because it suggests that two people eating the same licorice-containing diet could experience substantially different exposure to the parent compound and its microbial derivatives.

The fermentation experiments produced a second, equally important observation. When licochalcone A was present, microbial biomass grew more vigorously than in controls, with optical density readings at 24 hours reaching 0.83 compared with 0.52 in untreated cultures, and the pH of the cultures dropped to around 5.5 versus roughly 6.4 in controls, a highly significant difference. Lower intestinal pH is generally considered a hallmark of a healthier microbial environment, favoring beneficial commensals while suppressing opportunistic pathogens. Gas chromatography–mass spectrometry confirmed the metabolic significance of this shift: concentrations of acetic, propionic, butyric, and isobutyric acids all rose significantly after 24 hours, with propionate and butyrate showing the most pronounced increases. These short-chain fatty acids are among the most consequential metabolites the gut microbiota produces, fueling colonocytes, reinforcing the intestinal barrier, enhancing insulin sensitivity, and exerting anti-inflammatory effects throughout the body.

Using liquid chromatography coupled with tandem mass spectrometry, the team then hunted for the chemical fingerprints of microbial transformation. Licochalcone A displays a protonated molecular ion at m/z 339.1; after 48 hours of anaerobic fermentation, a new ion appeared at m/z 355.2, a mass increase of 16 daltons that pointed to a single hydroxylation event. The new metabolite eluted slightly earlier than the parent compound, consistent with its increased polarity, and comparison with an authentic reference standard of 3-hydroxylicochalcone A confirmed matching retention time and fragmentation patterns. Remarkably, this metabolite, abbreviated 3-HLA, appeared consistently across all four donors, suggesting that the transformation is mediated by a conserved microbial capability rather than a quirk of one person’s microbiome. Because many dietary polyphenols must be converted by gut bacteria before they can reach systemic circulation, the identification of 3-HLA establishes microbial metabolism as an additional regulatory layer governing the bioavailability and physiological impact of licochalcone A.

With community-level degradation established, the researchers turned to the strain level. Seventeen bacterial species were randomly isolated from human fecal samples, deliberately without pre-selecting for degradation ability, and each was challenged with licochalcone A under anaerobic conditions. Degradation capacity varied enormously. Escherichia coli, Collinsella aerofaciens, Clostridium innocuum, and Clostridium butyricum all performed respectably, removing roughly 80 to 88 percent of the compound, while Enterococcus faecium, Enterococcus faecalis, and Bacteroides vulgatus managed less than 25 percent. But the standout was Bifidobacterium longum subsp. suillum, a subspecies never before implicated in natural product degradation and, according to the authors, never previously isolated from human feces in the context of chalcone metabolism. Strain AA-55, as the isolate is designated, degraded approximately 90 percent of licochalcone A within 48 hours, and its growth actually accelerated during the exponential phase when the compound was present.

To understand how this bacterium accomplishes the feat, the team sequenced its entire genome. The circular chromosome of strain AA-55 spans 2,250,570 base pairs with a G+C content of 59.76 percent and encodes 1,841 proteins, along with five CRISPR loci and a compact set of RNA genes. Functional annotation revealed substantial enrichment of genes associated with xenobiotic biodegradation and metabolism, secondary metabolite biosynthesis and catabolism, and oxidoreductase catalytic activity, all categories consistent with a capacity to chemically transform structurally diverse exogenous compounds. The genome also carries 71 carbohydrate-active enzymes, including 45 glycoside hydrolases and 14 glycosyltransferases. The authors are careful to note, however, that genomic annotation alone cannot prove which enzymes perform the hydroxylation; genetic knockouts, enzyme purification, and heterologous expression studies will be needed to pin down the exact molecular machinery.

Untargeted metabolomics added a dynamic dimension to the story. When cultures of strain AA-55 were exposed to licochalcone A and sampled at 0, 6, and 24 hours, principal component and discriminant analyses showed complete metabolic segregation between exposed and control groups, with the first two principal components explaining over 62 percent of the variance. At 6 hours, 227 metabolites were significantly upregulated and 582 downregulated; by 24 hours the figures were 280 and 675. Pathway enrichment centered on amino acid metabolism, nucleotide turnover, the TCA cycle, and ABC transporters, indicating that degrading licochalcone A is not an isolated enzymatic side reaction but a process woven into the bacterium’s broader metabolic reprogramming. Among the altered metabolites were glycoisoflavanone, licoagroside B, and deoxyphomalone, compound classes previously associated with biological activity, though their specific health effects remain uncharacterized.

Perhaps the most ecologically intriguing finding came from co-culture experiments. Akkermansia muciniphila and Bacteroides ovatus, two species of considerable interest in gut health research, could barely degrade licochalcone A on their own. But when the researchers grew them in culture supernatant harvested from strain AA-55 fermenting the compound, both species proliferated dramatically, with 2.3-fold and 3-fold increases in growth respectively compared with vehicle-conditioned medium. In other words, the primary degrader’s metabolic byproducts function as cross-feeding currency that sustains secondary consumers, echoing the well-documented prebiotic behavior of inulin and fructooligosaccharides, where fiber-fermenting pioneers feed the rest of the community. This positions licochalcone A not merely as a pharmacological flavonoid but as a potential prebiotic-like ecological modulator capable of reshaping gut community structure through cooperative metabolism.

In vivo validation in mice lent the laboratory findings physiological weight. Oral administration of licochalcone A at 50 milligrams per kilogram to conventional C57BL/6 mice, followed by 16S rRNA gene sequencing of fecal samples at baseline, 6, 24, and 48 hours, revealed transient shifts in microbial composition: Bacteroidota rose at 6 and 24 hours while Bacillota dipped early, and taxa including Dubosiella, Allobaculum, and Bifidobacterium increased in relative abundance at later time points. These results align with earlier reports that licochalcone A promotes beneficial taxa in models of colitis and type 2 diabetes, though the authors caution that the dose used here exceeds typical human dietary exposure and that the absence of a vehicle-gavage control leaves room for handling effects.

The study’s limitations are candidly acknowledged: the human cohort comprised only four young men, the co-culture system simplifies the gut’s ecological complexity, and the biological function of 3-HLA in the body remains to be demonstrated. Even so, the work marks a genuine advance, revealing for the first time that bifidobacteria can drive chalcone biotransformation and identifying a specific strain whose metabolic appetite may determine how much active compound, and which derivatives, a licorice lover actually absorbs. As interest in microbiota-targeted functional foods accelerates, knowing which gut residents process licochalcone A, and how their activity ripples through the microbial food web, could prove essential for designing interventions that harness licorice’s ancient therapeutic promise with modern precision.

Subject of Research: Microbial degradation and biotransformation of the licorice flavonoid licochalcone A by the human gut microbiota

Article Title: Degradation and biotransformation of Licochalcone A by the human gut microbiota: Role of Bifidobacterium longum subsp . Suillum AA-55

Article References: Degradation and biotransformation of Licochalcone A by the human gut microbiota: Role of Bifidobacterium longum subsp . Suillum AA-55. (n.d.). https://doi.org/10.1016/j.jafr.2026.103299

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103299

Keywords: licochalcone A, gut microbiota, Bifidobacterium longum, licorice, 3-hydroxylicochalcone A, biotransformation, short-chain fatty acids, cross-feeding, polyphenols, metabolomics, prebiotic, functional foods