Expression of the pyr operon of Lactobacillus plantarum is regulated by inorganic carbon availability through a second regulator, PyrR2, homologous to the pyrimidine-dependent regulator PyrR1.
Inorganic carbon (IC), such as bicarbonate or carbon dioxide, stimulates the growth of Lactobacillus plantarum. At low IC levels, one-third of natural isolated L. plantarum strains are nutritionally dependent on exogenous arginine and pyrimidine, a phenotype previously defined as high-CO2-requiring (HCR) prototrophy. IC enrichment significantly decreased the amounts of the enzymes in the pyrimidine biosynthetic pathway encoded by the pyrR1BCAa1Ab1DFE operon, as demonstrated by proteomic analysis. Northern blot and reverse transcription-PCR experiments demonstrated that IC levels regulated pyr genes mainly at the level of transcription or RNA stability. Two putative PyrR regulators with 62% amino acid identity are present in the L. plantarum genome. PyrR1 is an RNA-binding protein that regulates the pyr genes in response to pyrimidine availability by a mechanism of transcriptional attenuation. In this work, the role of PyrR2 was investigated by allelic gene replacement. Unlike the pyrR1 mutant, the DeltapyrR2 strain acquired a demand for both pyrimidines and arginine unless bicarbonate or CO2 was present at high concentrations, which is known as an HCR phenotype. Analysis of the IC- and pyrimidine-mediated regulation in pyrR1 and pyrR2 mutants suggested that only PyrR2 positively regulates the expression levels of the pyr genes in response to IC levels but had no effect on pyrimidine-mediated repression. A model is proposed for the respective roles of PyrR1 and PyrR2 in the pyr regulon expression.
Arsène-Ploetze
Florence
F
UMR7156 Université Louis Pasteur/CNRS, Génétique Moléculaire, Génomique, Microbiologie, Département Microorganismes, Génomes, Environnement, 28 Rue Goethe, 67083 Strasbourg, France.
Kugler
Valérie
V
Martinussen
Jan
J
Bringel
Françoise
F
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001639:Bicarbonates / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D007287:Inorganic Chemicals / Q000378:metabolism; D048191:Lactiplantibacillus plantarum / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D008969:Molecular Sequence Data; D009876:Operon; D010430:Pentosyltransferases / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA
D001426:Bacterial Proteins; D001639:Bicarbonates; D007287:Inorganic Chemicals; D011743:Pyrimidines; D012097:Repressor Proteins; D002245:Carbon Dioxide; D002244:Carbon; D010430:Pentosyltransferases; C098851:PyrR protein, bacteria; C030986:pyrimidine