AexB is an aromatic amino acid exporter that functions as a metabolic safety valve

exacerbated growth defects under excess tryptophan conditions, likely due to feedback inhibition of aromatic amino acid synthesis pathways. Our findings reveal that AexB is an aromatic amino acid exporter that functions as a metabolic safety valve. IMPORTANCE: Identification and characterization of amino acid exporters is a broadly relevant topic. Amino acid synthesis is energetically costly, and thus functional relevance for their export is unintuitive. Identification of the molecular components that allow export may offer new engineering opportunities to improve biomanufacturing and metabolic engineering. Characterization of these exporters may also provide a more complete understanding of the human microbiome where amino acids, especially tryptophan, have been established as nodes of crosstalk between host and microbiota.