The ilvGMEDA operon is regulated by transcription attenuation in Vibrio alginolyticus ZJ-T

Bacteria synthesize amino-acids according to their availability in the environment or within the host in the case of pathogens. We explored the regulation of the biosynthesis of branched-chain amino acids (BCAAs: L-Leucine, L-Valine and L-Isoleucine) in Vibrio alginolyticus , a marine fish and shellfish pathogen and an emerging opportunistic human pathogen. In this species, the ilvGMEDA operon encodes the main pathway for biosynthesis of BCAAs. Its upstream regulatory region shows no sequence similarity to the corresponding region in Escherichia coli or other Enterobacteriaceae and yet, we show that this operon is regulated by transcription attenuation. The translation of a BCAA rich peptide encoded upstream of the structural genes provides an adaptive response similar to the E. coli canonical model. This study of a non-model Gram-negative organism highlights the mechanistic conservation of transcription attenuation despite the absence of primary sequence conservation. Importance This study analyzes the regulation of the biosynthesis of branched-chain amino-acids (Leucine, Valine, Isoleucine) in Vibrio alginolyticus , a marine bacterium pathogen to fish and humans. The results highlight the conservation of the main regulatory mechanism with this of the enterobacterium Escherichia coli , suggesting that such mechanism has appeared early during the evolution of Gram negative bacteria, allowing adaptation to a wide range of environments.