Pleiotropic transcriptional repressor CodY senses the intracellular pool of branched‐chain amino acids in Lactococcus lactis

Abstract

SummaryProteolysis is essential for supplying Lactococcus lactis with amino acids during growth in milk. Expression of the major components of the L. lactis proteolytic system, including the cell wall proteinase (PrtP), the oligopeptide transport system (Opp) and at least four intracellular peptidases (PepO1, PepN, PepC, PepDA2), was shown previously to be controlled negatively by a rich nitrogen source. The transcription of prtP, opp±pepO1, pepN and pepC genes is regulated by dipeptides in the medium. Random insertion mutants derepressed for nitrogen control in the expression of the oligopeptide transport system were isolated using an opp±lacZ fusion. A third of the mutants were targeted in the same locus. The product of the inactivated gene shared 48% identity with CodY from Bacillus subtilis, a pleiotropic repressor of the dipeptide permease operon (dpp) and several genes including genes involved in amino acid degradation and competence induction. The signal controlling CodY-dependent repression was searched for by analysing the response of the opp±lux fusion to the addition of 67 dipeptides with different amino acid compositions. Full correlation was found between the dipeptide content in branched-chain amino acids (BCAA; isoleucine, leucine or valine) and their ability to mediate the repression of opp±pepO1 expression. The repressive effect resulting from specific regulatory dipeptides was abolished in L. lactis mutants affected in terms of their transport or degradation into amino acids, showing that the signal was dependent on the BCAA pool in the cell. Lastly, the repression of opp±pepO1 expression was stronger in a mutant unable to degrade BCAAs, underlining the central role of BCAAs as a signal for CodY activity. This pattern of regulation suggests that, in L. lactis and possibly other Gram-positive bacteria, CodY is a pleiotropic repressor sensing nutritional supply as a function of the BCAA pool in the cell.

Branched chain aldehydes: production and breakdown pathways and relevance for flavour in foods

“…Extracellular molecules can influence the regulation of several reactions. As stated earlier, isoleucine is able to regulate the amino acid metabolism via CodY (Guedon et al 2001;Chambellon and Yvon 2003). Adding isoleucine to the cheese matrix should theoretically lead to lower 3-methyl butanal levels by high-3-methyl butanal producing strains.…”

Toxin-Antitoxin Systems of Mycobacterium smegmatis Are Essential for Cell Survival

“…Analysis of the intracellular metabolite profile revealed significant variations in the intracellular levels of the branched-chain amino acids leucine and isoleucine. The intracellular concentration of branchedchain amino acids in bacteria has been linked to the nutritional supply and physiological state of the cell (72,73), as well as serving a central role in linking catabolism with anabolism (74). Isoleucine was not detected in the ⌬TA triple mutant, and high levels of norleucine were detected.…”

The Lactococcus lactis CodY Regulon

“…L. lactis CodY exerts strong repressing activity in rapidly growing cells in media containing excess nitrogen (15). Therefore, the cells used for the transcriptional analyses were cultured in GM17 medium and harvested in the exponential phase of growth.…”