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Lactobacillus plantarum response to inorganic carbon concentrations: PyrR₂-dependent and -independent transcription regulation of genes involved in arginine and nucleotide metabolism

¹ CNRS, UMR7156, Génétique Moléculaire, Génomique Microbiologie, Département Microorganismes, Génomes, Environnement, 28 Rue Goethe, 67083 Strasbourg, France
² Université Louis-Pasteur Strasbourg-I, Strasbourg, France
³ CNRS, FRC 1589, Plateforme Protéomique Esplanade, 15 Rue René Descartes, 67084 Strasbourg, France

Correspondence
Florence Arsène-Ploetze
florence.ploetze{at}gem.u-strasbg.fr

Lactobacillus plantarum susbp. plantarum is a capnophilic Gram-positive heterotroph with optimal growth in 4 % CO₂-enriched air. At low inorganic carbon (C_i) concentrations, the pyr genes encoding the enzymes of the pyrimidine biosynthetic pathway were overexpressed, in agreement with a previous study showing that these genes are regulated at the transcription level in response to C_i via a PyrR₂-mediated mechanism. A previous study of high-CO₂-requiring (HCR) mutants revealed an unknown genetic link between arginine regulation and C_i-dependent nutritional needs. To better understand L. plantarum's adaptation to C_i availability, additional C_i-responsive genes were sought in the arginine biosynthetic pathway (arg and car genes) using slot-blot hybridization and a proteomic differential 2D gel electrophoresis (DIGE) global approach. Besides the nine pyr-encoded proteins, 16 new Icr (inorganic-carbon-regulated) proteins accumulated differentially in response to C_i availability, suggesting that the C_i response involves several metabolic pathways and adaptation processes. Among these Icr proteins only argininosuccinate lyase, encoded by argH, was involved in arginine biosynthesis. Three proteins involved in the purine biosynthetic pathway and nucleotide conversion, adenylate kinase (Adk), GMP synthase (GuaA), and IMP dehydrogenase (GuaB), accumulated differentially in response to changes in C_i levels. Expression of the Icr protein-encoding genes argH and guaB was regulated at the transcription level or by RNA stability in response to C_i availability, as previously demonstrated for the pyr genes. However, PyrR₂ was not essential for the C_i-regulated transcription of argH and guaB, demonstrating that PyrR₂ modulates only a subset of C_i-regulated genes. These results suggest that the C_i response may involve at least two regulatory mechanisms in L. plantarum.

A supplementary figure showing the results of differential proteomic analysis in response to C_i availability is available with the online version of this paper.