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Lactobacillus plantarum susbp, plantarum is a capnophilic Gram-positive heterotroph with optimal growth in 4% C[O.sub.2]-enriched air. At low inorganic carbon ([C.sub.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.sub.i] via a Pyr[R.sub.2]-mediated mechanism. A previous study of high-C[O.sub.2]-requiring (HCR) mutants revealed an unknown genetic link between arginine regulation and [C.sub.i]-dependent nutritional needs. To better understand L. plantarum's adaptation to [C.sub.i] availability, additional [C.sub.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 lcr (inorganic-carbon-regulated) proteins accumulated differentially in response to [C.sub.i] availability, suggesting that the [C.sub.i] response involves several metabolic pathways and adaptation processes. Among these lcr 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.sub.i] levels. Expression of the lcr protein-encoding genes argH and guaB was regulated at the transcription level or by RNA stability in response to [C.sub.i] availability, as previously demonstrated for the pyr genes. However, Pyr[R.sub.2] was not essential for the [C.sub.i]-regulated transcription of argH and guaB, demonstrating that Pyr[R.sub.2] modulates only a subset of [C.sub.i]-regulated genes. These results suggest that the [C.sub.i] response may involve at least two regulatory mechanisms in L. plantarum.

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-C[O.sub.2]-requiring (HCR) prototrophy. IC enrichment significantly decreased the amounts of the enzymes in the pyrimidine biosynthetic pathway encoded by the pyr[R.sub.1]BC[Aa.sub.1][Ab.sub.1]DFE 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. Pyr[R.sub.1] 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 Pyr[R.sub.2] was investigated by allelic gene replacement. Unlike the pyr[R.sub.1] mutant, the [DELTA]pyr[R.sub.2] strain acquired a demand for both pyrimidines and arginine unless bicarbonate or C[O.sub.2] was present at high concentrations, which is known as an HCR phenotype. Analysis of the IC- and pyrimidine-mediated regulation in [pyrR.sub.1] and [pyrR.sub.2] mutants suggested that only Pyr[R.sub.2] 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 Pyr[R.sub.1] and Pyr[R.sub.2] in the pyr regulon expression.

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 ΔpyrR2 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. [ABSTRACT FROM AUTHOR]

The article discusses the results of the study concerning the response of Lactobacillus plantarum to inorganic carbon concentrations. It mentions that the pyr genes encoding the enzymes of the pyrimidine biosynthetic pathway were overexpressed at the low inorganic carbon concentration. Furthermore, lcr protein-encoding genes argH and guaB expression was regulated at the transcriptiion level or by RNA stability in response to carbon concentration availability. The result suggests that the response of carbon concentration may involve with two regulatory mechanism in L. plantarum.