Phocaeicola

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.

Taxonomy

  • 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 huang 2024 fmt pcos metabolic ovarian dysfunction. 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 huang 2024 fmt pcos metabolic ovarian dysfunction.

Type 2 Diabetes (Disease-Discriminating)

Phocaeicola is identified as a key disease-discriminating taxon in T2D multi-omics analysis al bataineh 2023 multi omics microbiome metabolome t2d fiber and in metagenomic studies of diabetes with cardiovascular comorbidity zhang 2026 metagenomic gut microbiome diabetes mi.

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 bibbo 2025 fmt capsules ms case report, demonstrating its capacity for rapid colonization and potential role in microbiome-based MS interventions.

Key Studies

Cross-References

Related Articles