identifier: traitmech:000210 label: BREX system definition: A genomics trait describing possession of a bacteriophage exclusion defense system that uses host DNA methylation to discriminate self from non-self and inhibit phage DNA replication. definition_source: DOI:10.15252/embj.201489455 trait_category: GENOMICS term_kind: CLASS mapping_status: PROPOSED parent_traits: - traitmech:000209 synonyms: - synonym_text: bacteriophage exclusion synonym_type: EXACT_SYNONYM source: DOI:10.15252/embj.201489455 - synonym_text: bacteriophage exclusion system synonym_type: EXACT_SYNONYM source: DOI:10.1128/AEM.01001-19 evidence: - reference: DOI:10.15252/embj.201489455 snippet: We denote this novel defense system BREX (Bacteriophage Exclusion) and show that it allows phage adsorption but blocks phage DNA replication notes: Goldfarb et al. define BREX as a bacteriophage-exclusion defense system and distinguish its post-adsorption block from receptor-loss and phage-adsorption phenotypes. - reference: DOI:10.15252/embj.201489455 snippet: methylation on non-palindromic TAGGAG motifs in the bacterial genome guides self/non-self discrimination and is essential for the defensive function of the BREX system notes: Goldfarb et al. support the methylation-based self/non-self discrimination clause in the local definition. - reference: DOI:10.15252/embj.201489455 snippet: confers resistance to a broad range of phages, including both virulent and temperate ones notes: A Bacillus cereus six-gene BREX cassette conferred broad phage resistance when integrated into Bacillus subtilis, supporting BREX as a locus-encoded system trait. - reference: DOI:10.1128/AEM.01001-19 snippet: The bacteriophage exclusion (BREX) system is a novel prokaryotic defense system against bacteriophages notes: Hui et al. independently define bacteriophage exclusion as a prokaryotic defense system against bacteriophages. - reference: DOI:10.1128/AEM.01001-19 snippet: identified a complete cassette of a classic type I BREX system notes: Hui et al. identified a complete type I BREX cassette in the Lactobacillus casei Zhang genome. canonical_examples: - taxon_id: NCBITaxon:498216 taxon_label: Lacticaseibacillus casei str. Zhang note: The strain historically named Lactobacillus casei Zhang carries a complete type I BREX cassette whose pglX component is required for BREX-linked methylation and plasmid restriction phenotypes. reference: DOI:10.1128/AEM.01001-19 causal_graphs: - graph_id: brex_methylation_antiphage_defense title: BREX methylation guides antiphage discrimination description: Evidence-backed causal sketch linking a BREX locus to host-DNA methylation, self/non-self discrimination, and blocked phage-DNA replication. scope_status: MECHANISTIC scope_notes: The graph captures Goldfarb et al.'s experimentally supported host-methylation and post-adsorption phage-replication block without asserting that the molecular coupling between marked host DNA and blocked phage DNA is fully resolved. nodes: - node_id: phage_dna_replication label: phage DNA replication node_type: BIOLOGICAL_PROCESS description: Replication of invading bacteriophage DNA after host cell entry. - node_id: brex_locus label: BREX locus node_type: GENETIC_ELEMENT description: Multi-gene bacteriophage-exclusion cassette encoding the BREX defense system. - node_id: pglx_methyltransferase label: PglX adenine methyltransferase node_type: GENE_OR_PROTEIN description: Adenine-specific DNA methyltransferase component of type I BREX systems. grounding: InterPro:IPR047939 protein_examples: - uniprot_id: UniProtKB:P0DQP1 protein_label: Adenine-specific methyltransferase PglX gene_symbol: pglX taxon_id: NCBITaxon:498216 taxon_label: Lacticaseibacillus casei str. Zhang entry_status: REVIEWED retrieved_on: '2026-09-15' entry_version: 19 sequence_version: 1 role: L. casei Zhang PglX methylates BREX recognition motifs as the type I BREX adenine methyltransferase. evidence: - reference: DOI:10.1128/AEM.01001-19 snippet: this work confirmed that the L. casei Zhang pglX gene product is a functional adenine MTase that is an essential component of a type I BREX system notes: Hui et al. experimentally disrupted L. casei Zhang pglX; UniProt verifies the reviewed PglX accession. - node_id: host_dna_methylation label: BREX host DNA methylation node_type: BIOLOGICAL_PROCESS description: Methylation of host DNA at BREX recognition motifs. - node_id: self_nonself_discrimination label: BREX self/non-self discrimination node_type: BIOLOGICAL_PROCESS description: Methylation-guided discrimination of host DNA from unmodified invading phage DNA. - node_id: brex_system_trait label: BREX system node_type: TRAIT grounding: traitmech:000210 description: Possession of a genome-encoded bacteriophage exclusion defense system. - node_id: phage_defense_system label: phage defense system node_type: TRAIT grounding: traitmech:000209 description: Possession of one or more genome-encoded immune systems that inhibit bacteriophage infection. edges: - subject: brex_locus predicate: encodes object: pglx_methyltransferase description: Type I BREX loci encode PglX adenine methyltransferases. evidence: - reference: DOI:10.1128/AEM.01001-19 snippet: identified a complete cassette of a classic type I BREX system notes: The complete L. casei Zhang type I BREX cassette contains the pglX locus encoding PglX. - subject: pglx_methyltransferase predicate: contributes to predicate_id: RO:0002326 object: host_dna_methylation description: PglX methyltransferase activity methylates BREX recognition motifs in host DNA. evidence: - reference: DOI:10.1128/AEM.01001-19 snippet: this work confirmed that the L. casei Zhang pglX gene product is a functional adenine MTase notes: Hui et al. showed that pglX disruption removed m6A methylation at the recognition motif in L. casei Zhang. - subject: host_dna_methylation predicate: contributes to predicate_id: RO:0002326 object: self_nonself_discrimination description: Host DNA methylation guides BREX self/non-self discrimination. evidence: - reference: DOI:10.15252/embj.201489455 snippet: methylation on non-palindromic TAGGAG motifs in the bacterial genome guides self/non-self discrimination notes: Goldfarb et al. established methylation as the self/non-self mark for the characterized BREX system. - subject: self_nonself_discrimination predicate: confers predicate_id: METPO:2007700 object: brex_system_trait description: Methylation-guided self/non-self discrimination realizes the BREX defense trait. evidence: - reference: DOI:10.15252/embj.201489455 snippet: is essential for the defensive function of the BREX system notes: Goldfarb et al. established methylation-based self/non-self discrimination as essential to BREX defense. - subject: self_nonself_discrimination predicate: mitigates predicate_id: METPO:2007407 object: phage_dna_replication description: BREX methylation-guided discrimination blocks replication of unmethylated phage DNA. evidence: - reference: DOI:10.15252/embj.201489455 snippet: allows phage adsorption but blocks phage DNA replication notes: The edge records the observed post-adsorption replication block; the exact biochemical coupling remains a molecular knowledge gap. - subject: brex_system_trait predicate: is a predicate_id: rdfs:subClassOf object: phage_defense_system description: BREX possession is a methylation-based phage-defense system. evidence: - reference: DOI:10.15252/embj.201489455 snippet: We denote this novel defense system BREX (Bacteriophage Exclusion) notes: Goldfarb et al. place BREX in the phage defense system family. discussions: - discussion_id: brex-molecular-coupling-gap prompt: Resolve the molecular coupling between BREX-guided host methylation and phage-DNA replication arrest before adding more specific BREX mechanism edges. kind: KNOWLEDGE_GAP status: OPEN rationale: Goldfarb et al. showed that methylation is essential and that BREX blocks phage DNA replication after adsorption, but the exact biochemical coupling between the methylation mark and blocked phage replication remains insufficient for a more specific causal edge. posed_by: codex posed_date: '2026-09-15' curation_history: - timestamp: '2026-09-15T08:40:00Z' curator: codex action: MINTED_TRAITMECH_ID changes: Minted BREX system as a DOI-backed GENOMICS TraitRecord under the phage defense system parent after an ignored-and-hidden duplicate review found no exact live TraitMech, METPO, or prior proposal record; the replacement placeholder is reserved in proposals/metpo_traitmech_v87. llm_assisted: true