Relative abundance of faecal Bacteroides

Where it participates (unsigned role)

1. Co-culture was used to isolate KLE1738 which required the presence of Bacteroides fragilis to grow, bioassay-driven purification of the supernatant led to isolation of the growth factor which surprisingly is the major inhibitory neurotransmitter GABA, GABA was the only tested nutrient that supported the growth of KLE1738, a variety of GABA-producing bacteria were isolated and Bacteroides species produced large quantities of GABA, transcriptome analysis of human stool from healthy individuals showed that GABA-producing pathways are actively expressed by Bacteroides, Parabacteroides and Escherichia species, and relative abundance levels of faecal Bacteroides are negatively correlated with brain signatures associated with depression.

   Bacteroides fragilis → Gamma-aminobutyric acid source_derived_draftungraded
   Experimental context and source evidence

   evidence_span

   {"source_cache": "artifacts/gaba-research/30531975.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c5ec17a6d5ab61a71d407f753583383c556fb07e10434eb3a3c7b42e4d0953f9", "start_char": 0, "end_char": 1773, "text_sha256": "c5ec17a6d5ab61a71d407f753583383c556fb07e10434eb3a3c7b42e4d0953f9"}

   experimental_model

   Co-culture isolation with bioassay-driven purification, genome-based metabolic modelling, stool transcriptomics and brain imaging

   exposure

   A gut isolate that grows only in the presence of another species, and the growth factor it requires

   limitations

   The correlation with depression imaging is observational and the causal direction is not established. The bacteriology is direct.

   nutrient_topic

   GABA research collection; topical membership is not evidence of a direct clinical effect, and the sign of a GABA response depends on the chloride gradient of the cell it was measured in. · Gamma-aminobutyric acid

   organism

   Human

   plain_language

   One gut bacterium cannot grow without this molecule and another makes it in quantity, and the human gut expresses both halves.

   primary_references

   [gb-p30531975] GABA-modulating bacteria of the human gut microbiota. (2019). https://pubmed.ncbi.nlm.nih.gov/30531975/ DOI: 10.1038/s41564-018-0307-3

   tissue_or_cell_type

   Gut microbiota and brain

   GABA: a ligand with no sign of its own, the cofactor that limits its synthesis, the barrier that keeps it out of the brain, and the immune settings where the same molecule protects and harms (2026-09-22) · lines 495–506

   AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Co-culture isolation with bioassay-driven purification, genome-based metabolic modelling, stool transcriptomics and brain imaging · source_derived_draft · unverified_draft

   ### gb-gut-bacteria-make-and-consume-gaba Co-culture was used to isolate KLE1738 which required the presence of Bacteroides fragilis to grow, bioassay-driven purification of the supernatant led to isolation of the growth factor which surprisingly is the major inhibitory neurotransmitter GABA, GABA was the only tested nutrient that supported the growth of KLE1738, a variety of GABA-producing bacteria were isolated and Bacteroides species produced large quantities of GABA, transcriptome analysis of human stool from healthy individuals showed that GABA-producing pathways are actively expressed by Bacteroides, Parabacteroides and Escherichia species, and relative abundance levels of faecal Bacteroides are negatively correlated with brain signatures associated with depression. Condition category: normal nutrient_topic: GABA research collection; topical membership is not evidence of a direct clinical effect, and the sign of a GABA response depends on the chloride gradient of the cell it was measured in. plain_language: One gut bacterium cannot grow without this molecule and another makes it in quantity, and the human gut expresses both halves. organism: Human tissue_or_cell_type: Gut microbiota and brain experimental_model: Co-culture isolation with bioassay-driven purification, genome-based metabolic modelling, stool transcriptomics and brain imaging limitations: The correlation with depression imaging is observational and the causal direction is not established. The bacteriology is direct. exposure: A gut isolate that grows only in the presence of another species, and the growth factor it requires evidence_span: {"source_cache": "artifacts/gaba-research/30531975.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c5ec17a6d5ab61a71d407f753583383c556fb07e10434eb3a3c7b42e4d0953f9", "start_char": 0, "end_char": 1773, "text_sha256": "c5ec17a6d5ab61a71d407f753583383c556fb07e10434eb3a3c7b42e4d0953f9"} [gb-p30531975] GABA-modulating bacteria of the human gut microbiota. (2019). https://pubmed.ncbi.nlm.nih.gov/30531975/ DOI: 10.1038/s41564-018-0307-3

   Complete structured claim and evidence