Flavonifractor

Taxonomy and Classification#

Flavonifractor plautii (formerly Clostridium orbiscindens) is the type and sole well-characterized species. Member of Ruminococcaceae within Clostridiales (Firmicutes phylum), placing it phylogenetically among the anaerobic fermenters of complex carbohydrates and plant-derived compounds. The genus name reflects its defining capability: flavoni- (flavonoid) + fractor (breaker).

Reclassification from Clostridium reflects broader reorganization of the paraphyletic Clostridium genus based on 16S rRNA phylogeny.

Metal Dependencies and Enzyme Biochemistry#

Flavonifractor encodes a suite of metal-dependent oxidoreductases that underpin its unique metabolic niche. Iron-dependent cytochrome b-like flavoprotein: Central to the electron transport chain supporting anaerobic aromatic ring reduction. Iron serves as the electron carrier within the heme cofactor, enabling the ring-opening reactions that deactivate flavonoids.

Cobalt-dependent corrinoid enzymes: Cobalt-containing B12-like cofactors participate in the reductive dehalogenation and carbon skeleton rearrangements involved in phenolic acid catabolism downstream of ring cleavage.

Enoate reductase (2-enoate reductase): An iron-sulfur cluster enzyme that reduces the C2=C3 double bond in flavonoids, a key step in the deactivation of chalcones and flavanones including naringenin and eriodictyol.

Chalcone isomerase: Converts chalcones to flavanones, feeding them into the reductase pathway.

The iron and cobalt requirements explain why Flavonifractor can thrive in iron-replete dysbiotic environments: conditions like CKD and inflammatory bowel states where iron dysregulation is common provide the cofactor availability that fuels its metabolic machinery.

In the Healthy Gut#

Low-abundance member of the Ruminococcaceae community in health; ecological competition from Butyrate producers like Faecalibacterium prausnitzii and Roseburia limits its expansion.

Functions as a minor scavenger of plant polyphenols not absorbed in the small intestine, contributing to the diversity of phenolic acid metabolites in the gut.

In a balanced community, flavonoid degradation by Flavonifractor is offset by the abundance of short-chain fatty acid producers, maintaining net anti-inflammatory tone.

In Dysbiosis#

Competitive release: When Faecalibacterium prausnitzii and butyrate producers decline—as in fibromyalgia, CKD, and post-antibiotic states—Flavonifractor expands into the vacated niche.

Polyphenol erosion: Its expansion removes a key class of dietary anti-inflammatory agents precisely when the patient's inflammatory burden is already elevated.

Uremic toxin contribution: In CKD, Flavonifractor enrichment correlates with progression.^{[2]Wang 2023 — Perturbed Gut Microbiome and Metabolomes Across CKD SeverityWang, Li, Zhang et al. · 2023Open reference 2 ↓}

The phenolic acids produced from flavonoid degradation can serve as substrates for further microbial transformation into indole-related uremic toxins (indoxyl sulfate precursors via aromatic amino acid catabolism overlap), potentially contributing to uremic toxin burden.

Fibromyalgia#

Flavonifractor is one of the most consistently enriched taxa in fibromyalgia microbiome studies.

Significantly enriched in fibromyalgia patients versus healthy controls, with abundance correlating directly with symptom severity scores.^{[1]Minerbi 2019 — Altered Microbiome Composition in FibromyalgiaMinerbi A, Gonzalez E, Brereton NJB et al. · 2019Open reference 1 ↓} Confirmed as a reproducible finding in a meta-analysis of gut Dysbiosis across chronic pain conditions.^{[3]Goudman 2024 — Gut Dysbiosis in Chronic Pain (Meta-Analysis)Goudman et al. · 2024Open reference 3 ↓}

FMT from fibromyalgia patients to germ-free mice induced mechanical pain hypersensitivity, implicating the microbiome causally—and Flavonifractor is among the enriched taxa transferred in those experiments.^{[4]Shtrozberg 2025 — Gut Microbiome in Fibromyalgia (Review)Shtrozberg et al. · 2025Open reference 4 ↓}

The co-depletion of Faecalibacterium prausnitzii and Bifidobacterium alongside Flavonifractor enrichment creates a dual loss: loss of butyrate-mediated anti-nociception and loss of flavonoid-mediated anti-Metal-Driven Inflammation.

Chronic Kidney Disease#

Flavonifractor enrichment increases with CKD staging; enriched alongside Citrobacter as a dysbiotic marker while Faecalibacterium prausnitzii and Eubacterium rectale are depleted.^{[2]Wang 2023 — Perturbed Gut Microbiome and Metabolomes Across CKD SeverityWang, Li, Zhang et al. · 2023Open reference 2 ↓}

The combined microbiome + metabolite diagnostic model achieving AUC 0.972 for mild CKD detection in this cohort included Flavonifractor among the discriminating features—meaning its abundance has early diagnostic signal, detectable before conventional biomarkers like creatinine change.

Flavonifractor also appears in ESRD (end-stage renal disease) microbiome analyses as part of the uremic dysbiosis pattern.^{[5]Zhang 2023 — Metagenome-Wide Analysis of ESRD Microbiome and Uremic ToxinsZhang, Liao, Mei et al. · 2023Open reference 5 ↓}

Multiple Sclerosis#

Present in MS-associated gut dysbiosis signatures, consistent with its pattern of enrichment in neuroinflammatory conditions.^{[6]The Gut Microbiota in Multiple Sclerosis Varies with Disease ActivityThirion F, Sellebjerg F, Fan Y et al. · 2023Open reference 6 ↓} Its depletion of neuroprotective flavonoids may be particularly relevant in neuroinflammatory contexts where dietary polyphenols like quercetin have documented neuroprotective effects.

Autism Spectrum Disorder#

Identified in ASD-associated Gut Microbiome signatures in Chinese pediatric cohorts.^{[7]Wang 2023 — Gut Microbiota Signature in Children with ASD Who Suffered from Chronic Gastrointestinal SymptomsHui Wang, Shu Liu, Liqing Xie et al. · 2023Open reference 7 ↓} Whether this reflects a primary role or secondary enrichment driven by the restrictive dietary patterns common in ASD requires further investigation.