{"id":"61ff732e-b029-56c9-a0ef-52f5629946dd","stable_key":"1b599eb7-b22a-5fda-bcf0-9d92b5ae1311:gb-gut-bacteria-make-and-consume-gaba","predicate":"produces","statement":"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.","claim_class":"observational","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"d0ce9b3c-8500-549b-bd45-328ef6d29fe4","mechanism_event_label":"One gut bacterium cannot grow without this molecule and another makes it in quantity, and the human gut expresses both halves.","subject":{"id":"b4f38d31-8e45-5633-bd30-98cb16e08232","slug":"bacteroides-fragilis","display_name":"Bacteroides fragilis","entity_type_key":"organism"},"object":{"id":"d5b98fa8-0612-5a5a-aa3c-6cfd8ff88867","slug":"gaba","display_name":"Gamma-aminobutyric acid","entity_type_key":"small_molecule"},"evidence_count":1,"mechanism_event":{"id":"d0ce9b3c-8500-549b-bd45-328ef6d29fe4","stable_key":"1b599eb7-b22a-5fda-bcf0-9d92b5ae1311:gb-gut-bacteria-make-and-consume-gaba-event","event_type":"observed_intervention","label":"One gut bacterium cannot grow without this molecule and another makes it in quantity, and the human gut expresses both halves.","description":"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.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"4798a4b8-d972-5d52-a88e-eafbbe01dc0c","slug":"kle1738","display_name":"The gut isolate KLE1738","entity_type_key":"organism"},"role":"dependent_organism","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"c0f1051c-43f6-5193-bab7-02554337d974","slug":"faecal-bacteroides-abundance","display_name":"Relative abundance of faecal Bacteroides","entity_type_key":"cellular_process"},"role":"correlated_measure","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"b4f38d31-8e45-5633-bd30-98cb16e08232","slug":"bacteroides-fragilis","display_name":"Bacteroides fragilis","entity_type_key":"organism"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"d5b98fa8-0612-5a5a-aa3c-6cfd8ff88867","slug":"gaba","display_name":"Gamma-aminobutyric acid","entity_type_key":"small_molecule"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""}]},"contexts":[{"dimension":"evidence_span","value_text":"{\"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\"}","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Co-culture isolation with bioassay-driven purification, genome-based metabolic modelling, stool transcriptomics and brain imaging","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"A gut isolate that grows only in the presence of another species, and the growth factor it requires","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"The correlation with depression imaging is observational and the causal direction is not established. The bacteriology is direct.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"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.","comparator":null,"unit":null,"notes":"","entity":{"slug":"gaba","display_name":"Gamma-aminobutyric acid","entity_type_key":"small_molecule"}},{"dimension":"organism","value_text":"Human","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"One gut bacterium cannot grow without this molecule and another makes it in quantity, and the human gut expresses both halves.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[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","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Gut microbiota and brain","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"0334c8b0-e026-5a39-bb19-13d2a5e090b5","evidence_kind":"source_excerpt","locator":"Lines 495-506","start_line":495,"end_line":506,"excerpt":"### gb-gut-bacteria-make-and-consume-gaba\nCo-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.\nCondition category: normal\nnutrient_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.\nplain_language: One gut bacterium cannot grow without this molecule and another makes it in quantity, and the human gut expresses both halves.\norganism: Human\ntissue_or_cell_type: Gut microbiota and brain\nexperimental_model: Co-culture isolation with bioassay-driven purification, genome-based metabolic modelling, stool transcriptomics and brain imaging\nlimitations: The correlation with depression imaging is observational and the causal direction is not established. The bacteriology is direct.\nexposure: A gut isolate that grows only in the presence of another species, and the growth factor it requires\nevidence_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\"}\n[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","model_system":"Co-culture isolation with bioassay-driven purification, genome-based metabolic modelling, stool transcriptomics and brain imaging","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study 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","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"197c25bb-45fa-5e97-b3ab-2d2eff4e0d0a","stable_key":"import-1b599eb7-b22a-5fda-bcf0-9d92b5ae1311","title":"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)","document_type":"imported_text","citation_label":"AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text.","file_path":"","sha256":"07e36027ff70dbbe5563cddfa4758fd9b9b6eec148faecccafd476900b770456","revision_id":"a12d61de-f189-5bda-af3d-f31a1e61bccf","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}