A Gram-negative, obligate anaerobic genus within the phylum Bacteroidota (formerly Bacteroidetes) that was recently reclassified from Bacteroides based on phylogenomic evidence (Garcia-Lopez et al. , 2019).
The key species—Phocaeicola vulgatus (formerly Bacteroides vulgatus), P. dorei, P. massiliensis—are among the most abundant gut bacteria, yet the reclassification means that decades of Bacteroides literature must now be reinterpreted.
Phocaeicola has gained particular attention in PCOS research, where FMT experiments demonstrate that a Phocaeicola-enriched microbiota causally transfers the PCOS phenotype to germ-free mice.
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FMT from PCOS patients to germ-free mice recapitulates the full PCOS phenotype—insulin resistance, ovarian dysfunction, and obese-like phenotype. The transferred microbiome was enriched in Phocaeicola, mediterraneibacter, oscillospiraceae, and Lawsonibacter, establishing these taxa as potential causal mediators of the PCOS gut-ovarian axis.
Phocaeicola enrichment in PCOS fecal microbiota and its transfer of the PCOS phenotype via FMT provides some of the strongest causal evidence linking a specific taxon to an endocrine disorder.
Phocaeicola is identified as a key disease-discriminating taxon in T2D multi-omics analysis and in metagenomic studies of diabetes with cardiovascular comorbidity.
In a case report of FMT capsule treatment for MS, Phocaeicola appeared from 0% at baseline, peaking at 7.2% after treatment, demonstrating its capacity for rapid colonization and potential role in microbiome-based MS interventions.
(animal model/FMT)—PCOS phenotype transfer via Phocaeicola-enriched microbiota.
(cross-sectional)—T2D disease-discriminating taxon.
(case report)—Rapid colonization after FMT in MS patient.
(cross-sectional)—Key discriminative species in diabetes-MI comorbidity.
Contents
1. Taxonomy2. Metal Dependencies3. Key Enzymes and Metabolic Features4. Ecological Role5. Conditions Associated6. Key Studies7. Cross-ReferencesTaxonomy#
Genus Phocaeicola, family Bacteroidaceae, order Bacteroidales, class Bacteroidia, phylum Bacteroidota. Key species: P. vulgatus (formerly Bacteroides vulgatus), P. dorei, P. massiliensis, P. stercoris. Named after Phocaea (the ancient Greek name for Marseille, where the type strain was isolated).
The reclassification has clinical implications: studies citing "Bacteroides vulgatus" in disease associations are now describing Phocaeicola behavior, and the functional properties attributed to the old name carry forward to the new genus.
Metal Dependencies#
Iron. Like other Bacteroidota, Phocaeicola encodes TonB-dependent outer membrane receptors for iron acquisition. Iron-dependent fumarate reductase supports anaerobic respiration.
Phocaeicola species generally have moderate iron requirements, less aggressive than Enterobacteriaceae but sufficient to benefit from iron-replete inflammatory environments.
Key Enzymes and Metabolic Features#
Polysaccharide utilization loci (PUL): Phocaeicola encodes extensive PUL systems for degrading complex dietary and host-derived glycans. This is the hallmark metabolic capability of Bacteroidota and positions Phocaeicola as a primary carbohydrate degrader in the gut.
Beta-glucosidase: Hydrolyzes dietary plant glucosides; relevant to polyphenol and phytoestrogen metabolism. Succinate dehydrogenase: Iron-dependent enzyme in fumarate respiration, the primary anaerobic energy-generating pathway.
Ecological Role#
In the Healthy Gut#
Phocaeicola species are among the most abundant organisms in the human colon, typically comprising 5-15% of the total community. They serve as primary degraders of complex carbohydrates, producing succinate, acetate, and propionate as fermentation end products. Their extensive PUL repertoire allows them to exploit a wide range of dietary substrates.
In PCOS#
FMT from PCOS patients to germ-free mice recapitulates the full PCOS phenotype—insulin resistance, ovarian dysfunction, and obese-like phenotype.[1]Fecal microbiota transplantation from patients with polycystic ovary syndrome induces metabolic disorders and ovarian dysfunction in germ-free miceHuang F, Deng Y, Zhou M et al. · 2024Open reference 1 ↓ The transferred microbiome was enriched in Phocaeicola, Mediterraneibacter, Oscillospiraceae, and Lawsonibacter, establishing these taxa as potential causal mediators of the PCOS gut-ovarian axis.
Conditions Associated#
Polycystic Ovary Syndrome (Enriched—Causal Evidence)#
Phocaeicola enrichment in PCOS fecal microbiota and its transfer of the PCOS phenotype via FMT provides some of the strongest causal evidence linking a specific taxon to an endocrine disorder.[1]Fecal microbiota transplantation from patients with polycystic ovary syndrome induces metabolic disorders and ovarian dysfunction in germ-free miceHuang F, Deng Y, Zhou M et al. · 2024Open reference 1 ↓
Type 2 Diabetes (Disease-Discriminating)#
Phocaeicola is identified as a key disease-discriminating taxon in T2D multi-omics analysis[2]Al Bataineh 2023 — Multi-Omics Analysis of Gut Microbial Dysbiosis, Metabolomics, and Dietary Intake in Type 2 DiabetesMohammad Tahseen Al Bataineh, Axel Kunstner, Nihar Ranjan Dash et al. · 2023Open reference 2 ↓ and in metagenomic studies of diabetes with cardiovascular comorbidity.[3]A metagenomic study of the gut microbiome in patients with type 2 diabetes mellitus and myocardial infarctionHonghong Zhang, Changlin Zhai, Huilin Hu et al. · 2026Open reference 3 ↓
Multiple Sclerosis (FMT Colonizer)#
In a case report of FMT capsule treatment for MS, Phocaeicola appeared from 0% at baseline, peaking at 7.2% after treatment,[4]Case Report: Fecal microbiota transplantation via capsules ameliorated clinical outcomes in a patient with multiple sclerosisStefano Bibbò, Flavio De Maio, Fioravante Capone et al. · 2025Open reference 4 ↓ demonstrating its capacity for rapid colonization and potential role in microbiome-based MS interventions.
Key Studies#
[1]Fecal microbiota transplantation from patients with polycystic ovary syndrome induces metabolic disorders and ovarian dysfunction in germ-free miceHuang F, Deng Y, Zhou M et al. · 2024Open reference 1 ↓ (animal model/FMT)—PCOS phenotype transfer via Phocaeicola-enriched microbiota.[2]Al Bataineh 2023 — Multi-Omics Analysis of Gut Microbial Dysbiosis, Metabolomics, and Dietary Intake in Type 2 DiabetesMohammad Tahseen Al Bataineh, Axel Kunstner, Nihar Ranjan Dash et al. · 2023Open reference 2 ↓ (cross-sectional)—T2D disease-discriminating taxon.[4]Case Report: Fecal microbiota transplantation via capsules ameliorated clinical outcomes in a patient with multiple sclerosisStefano Bibbò, Flavio De Maio, Fioravante Capone et al. · 2025Open reference 4 ↓ (case report)—Rapid colonization after FMT in MS patient.
[3]A metagenomic study of the gut microbiome in patients with type 2 diabetes mellitus and myocardial infarctionHonghong Zhang, Changlin Zhai, Huilin Hu et al. · 2026Open reference 3 ↓ (cross-sectional)—Key discriminative species in diabetes-MI comorbidity.
Cross-References#
- Bacteroides vulgatus—the former classification; literature must be reinterpreted
- Mediterraneibacter—co-enriched in PCOS FMT microbiota
- Polycystic Ovary Syndrome—causal FMT evidence for PCOS phenotype transfer
- Type 2 Diabetes—disease-discriminating taxon
- Multiple Sclerosis—rapid colonizer after FMT
- Iron—TonB-dependent iron acquisition
References 4
Numbered by first appearance in the article, then reconciled with its declared source list.
- 1
Huang F, Deng Y, Zhou M et al. (2024). Fecal microbiota transplantation from patients with polycystic ovary syndrome induces metabolic disorders and ovarian dysfunction in germ-free mice. BMC Microbiology.
- 2
Mohammad Tahseen Al Bataineh, Axel Kunstner, Nihar Ranjan Dash et al. (2023). Al Bataineh 2023 — Multi-Omics Analysis of Gut Microbial Dysbiosis, Metabolomics, and Dietary Intake in Type 2 Diabetes. Scientific Reports.
- 3
Honghong Zhang, Changlin Zhai, Huilin Hu et al. (2026). A metagenomic study of the gut microbiome in patients with type 2 diabetes mellitus and myocardial infarction. Acta Diabetologica.
- 4
Stefano Bibbò, Flavio De Maio, Fioravante Capone et al. (2025). Case Report: Fecal microbiota transplantation via capsules ameliorated clinical outcomes in a patient with multiple sclerosis. Frontiers in Immunology.
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