ABSTRACT
Streptococcus pneumoniae is a fastidious obligate parasite requiring several amino acids for growth. Oligopeptide uptake mediated by the Ami ABC permease is therefore important for nutrition but this could not account for the highly pleiotropic phenotype exhibited by Ami mutants. The hypothesis that peptide transport plays a pivotal role in sensing environmental conditions and indirectly modulates the expression of several genes is discussed.
Subject(s)
Carrier Proteins/physiology , Lipoproteins/physiology , Streptococcus pneumoniae/enzymology , Bacterial Proteins/genetics , Bacterial Proteins/physiology , Carrier Proteins/genetics , DNA, Bacterial , Environment , Lipoproteins/genetics , Models, Genetic , Mutation , Phenotype , Regulatory Sequences, Nucleic Acid , Regulon , Streptococcus pneumoniae/geneticsABSTRACT
The Lactococcus lactis ccpA gene, encoding the global regulatory protein CcpA, was identified and characterized. Northern blot and primer extension analyses showed that the L. lactis ccpA gene is constitutively transcribed from a promoter that does not contain a cre sequence. Inactivation of the ccpA gene resulted in a twofold reduction in the growth rate compared with the wild type on glucose, sucrose and fructose, while growth on galactose was almost completely abolished. The observed growth defects could be complemented by the expression of either the L. lactis or the Bacillus subtilis ccpA gene. The disruption of the ccpA gene reduced the catabolite repression of the gal operon, which contains a cre site at the transcription start site and encodes enzymes involved in galactose catabolism. In contrast, CcpA activates the transcription of the cre-containing promoter of the las operon, encoding the glycolytic enzymes phosphofructokinase, pyruvate kinase and L-lactate dehydrogenase, because its transcription level was fourfold reduced in the ccpA mutant strain compared with the wild-type strain. The lower activities of pyruvate kinase and L-lactate dehydrogenase in the ccpA mutant strain resulted in the production of metabolites characteristic of a mixed-acid fermentation, whereas the fermentation pattern of the wild-type strain was essentially homolactic.
Subject(s)
Bacterial Proteins , DNA-Binding Proteins/metabolism , Gene Expression Regulation, Bacterial , Glycolysis , Lactococcus lactis/genetics , Operon , Repressor Proteins/metabolism , Base Sequence , Cloning, Molecular , DNA, Bacterial , DNA-Binding Proteins/genetics , Genes, Bacterial , L-Lactate Dehydrogenase/metabolism , Lactococcus lactis/growth & development , Molecular Sequence Data , Pyruvate Kinase/metabolism , Repressor Proteins/genetics , Transcriptional ActivationABSTRACT
The replication of two cryptic plasmids from Brevibacterium linens ATCC 9174 (pBL33) and Rhodococcus rhodochrous ATCC 4276 (pRC1) was investigated in Rhodococcus sp. R312 (formerly Brevibacterium sp. R312). The recombinant plasmids pSP33 (pBL33 derivative) and pSPC1 (pRC1 derivative) were found to be suitable for establishing new host-vector systems for Rhodococcus sp. R312. They all carry the Tn903 neomycin-resistance-encoding gene (aphI).
