Role of the crr-gene in glucose uptake by Escherichia coli

Starvation induces shrinkage of the bacterial cytoplasm

Environmental fluctuations are a common challenge for single-celled organisms; enteric bacteria such as Escherichia coli experience dramatic changes in nutrient availability, pH, and temperature during their journey into and out of the host. While the effects of altered nutrient availability on gene expression and protein synthesis are well known, their impacts on cytoplasmic dynamics and cell morphology have been largely overlooked. Here, we discover that depletion of utilizable nutrients results in shrinkage of E. coli's inner membrane from the cell wall. Shrinkage was accompanied by an ∼17% reduction in cytoplasmic volume and a concurrent increase in periplasmic volume. Inner membrane retraction after sudden starvation occurred almost exclusively at the new cell pole. This phenomenon was distinct from turgor-mediated plasmolysis and independent of new transcription, translation, or canonical starvation-sensing pathways. Cytoplasmic dry-mass density increased during shrinkage, suggesting that it is driven primarily by loss of water. Shrinkage was reversible: upon a shift to nutrient-rich medium, expansion started almost immediately at a rate dependent on carbon source quality. A robust entry into and recovery from shrinkage required the Tol-Pal system, highlighting the importance of envelope coupling during shrinkage and recovery. Klebsiella pneumoniae also exhibited shrinkage when shifted to carbon-free conditions, suggesting a conserved phenomenon. These findings demonstrate that even when Gram-negative bacterial growth is arrested, cell morphology and physiology are still dynamic.

Competition between two pathways for sugar uptake by the phosphoenolpyruvate-dependent sugar phosphotransferase system in Salmonella typhimurium

The interaction between the two pathways for glucose entry via the phosphoenolpyruvate:sugar phosphotransferase system, i.e. via enzyme II-A/II-B and enzymes II-BGlc/IIIGlc, was studied in Salmonella typhimurium. Thio-beta-D-glucoside and 5-thio-D-glucose were shown to be substrates of P-pyruvate:sugar phosphotransferase specific for enzyme II-BGlc both in intact cells and in toluene-treated cells of S. typhimurium. The activity of the II-A/II-B pathway was strongly inhibited by the presence of II-BGlc substrates. It is concluded that the two pathways compete for phosphoryl groups provided by P-pyruvate, and that under the conditions tested the flow of phosphoryl groups through enzyme I/HPr is the rate-limiting step in vivo of activity of the pathways studied. The results corroborate the proposed mechanism of the regulatory function of the P-pyruvate:sugar phosphotransferase system which predicts a net dephosphorylation of components of the P-pyruvate:sugar phosphotransferase in the presence of a substrate of P-pyruvate:sugar phosphotransferase.

Alteration of glucose transport and diauxic growth in 5-thio-D-glucose-resistant mutants of Azotobacter vinelandii

Spontaneous mutants of Azotobacter vinelandii defective for glucose utilization were selected as resistant to 5-thio-D-glucose. Mutant strains AM2, AM38, and AM39 exhibited longer generation times than the wild type when grown on glucose. Mutant strain AM2 also exhibited an altered Km and Vmax for glucose uptake. During acetate-glucose diauxie, glucose utilization in the 5-thio-D-glucose-resistant mutants was subject to severe inhibition by acetate. These mutants did not exhibit the normal glucose phase of diauxie. Transport studies during diauxie indicated that glucose uptake was not induced in mutant strain AM2. However, increasing the glucose concentration from 25 to 200 mM relieved the severe acetate inhibition, and under these conditions the mutant strain AM2 exhibited normal diauxie. Revertants of mutant strain AM2 exhibited normal glucose and diauxie growth. The results are discussed in terms of a model for acetate regulation of glucose utilization in A. vinelandii.

Role of IIIGlc of the phosphoenolpyruvate-glucose phosphotransferase system in inducer exclusion in Escherichia coli

The phosphoenolpyruvate-D-glucose phosphotransferase system of Enterobacteriaceae is thought to regulate the synthesis and activity of a number of catabolite uptake systems, including those for maltose, lactose, and glycerol, via the phosphorylation state of one of its components, IIIGlc. We have investigated the proposal by Kornberg and co-workers (FEBS Lett. 117(Suppl.):K28-K36, 1980) that not IIIGlc, but an unknown protein, the product of the iex gene, is responsible for the exclusion of the above-mentioned compounds from the cell. The iex mutant HK738 of Escherichia coli contains normal amounts of IIIGlc as measured by specific antibodies, in contrast to crr mutants that lack IIIGlc. The IIIGlc of the iex strain functions normally in glucose and methyl alpha-glucoside transport, and the specific activity in in vitro phosphorylation is approximately 60% of that of the parent. The IIIGlc activity of the iex strain is, however, heat labile, in contrast to the parental IIIGlc, suggesting that the mutant contains an altered IIIGlc. This is supported by the observation that IIIGlc from the iex strain cannot bind to the lactose carrier. Thus it cannot inhibit the carrier, and this explains why the uptake of non-phosphotransferase system compounds in an iex strain is resistant to phosphotransferase system sugars. The introduction of a plasmid containing a wild-type crr+ allele into the iex strain restores the iex phenotype to that of the iex+ parent. The IIIGlc produced from the plasmid in the iex strain is heat stable and binds normally to the lactose carrier. These results lead to the conclusion that the iex mutation is most likely allelic with crr and results in an altered, temperature-sensitive IIIGlc that is still able to function D-glucose and methyl alpha-glucoside uptake and phosphorylation and in the activation of adenylate cyclase, but is unable to bind to and inhibit the lactose carrier.

Characterization of factor IIIGLc in catabolite repression-resistant (crr) mutants of Salmonella typhimurium

crr mutants of Salmonella typhimurium are thought to be defective in the regulation of adenylate cyclase and a number of transport systems by the phosphoenolpyruvate-dependent sugar phosphotransferase system, crr mutants are also defective in the enzymatic activity of factor IIIGlc (IIIGlc), a protein component of the phosphotransferase system involved in glucose transport. Therefore, it has been proposed that IIIGlc is the primary effector of phosphotransferase system-mediated regulation of cell metabolism. We characterized crr mutants with respect to the presence and function of IIIGlc by using an immunochemical approach. All of the crr mutants tested had low (0 to 30%) levels of IIIGlc compared with wild-type cells, as determined by rocket immunoelectrophoresis. The IIIGlc isolated from one crr mutant was investigated in more detail and showed abnormal aggregation behavior, which indicated a structural change in the protein. These results supported the hypothesis that a crr mutation directly affects IIIGlc, probably by altering the structural gene of IIIGlc. Several crr strains which appeared to be devoid of IIIGlc in immunoprecipitation assays were still capable of in vitro phosphorylation and transport of methyl alpha-glucoside. This phosphorylation activity was sensitive to specific anti-IIIGlc serum. Moreover, the membranes of crr mutants, as well as those of wild-type cells, contained a protein that reacted strongly with our anti-IIIGlc serum. We propose that S. typhimurium contains a membrane-bound form of IIIGlc which may be involved in phosphotransferase system activity.

Isolation of IIIGlc of the phosphoenolpyruvate-dependent glucose phosphotransferase system of Salmonella typhimurium

We report a procedure for the isolation of IIIglc of Salmonella typhimurium, a protein component of the phosphoenolpyruvate-dependent sugar phosphotransferase system. IIIGlc is a soluble protein with a molecular weight of 21,000, as determined by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified protein is involved in the phosphoenolpyruvate-dependent phosphorylation of methyl alpha-glucoside in vitro. Its affinity for octyl-Sepharose may be an indication of the partial hydrophobic nature of IIIGlc. A specific antiserum against purified IIIGlc was prepared. Growth on different carbon sources did not affect the synthesis of IIIGlc, as determined by quantitative immunoelectrophoresis. Mutations which lower the adenosine 3',5'-phosphate level, such as cya and pts, do not alter the IIIGlc level. The closely related enteric bacteria Escherichia coli and Klebsiella aerogenes contain a protein factor which is closely related to IIIGlc of S. typhimurium, whereas Staphylococcus aureus does not.

Involvement of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system in regulation of transcription of catabolic genes

Synthesis of catabolite-sensitive enzymes is repressed in mutants defective in the general proteins (enzyme I and HPr) of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system (ptsI and ptsH mutations). To elucidate the mechanism of this phenomenon we constructed isogenic strains carrying pts mutations as well as different lesions of regulation of the lac operon or mutations affecting adenylate cyclase activity (cya mutation) and synthesis of cyclic AMP-receptor protein (crp mutation) Measurements of the differential rate of beta-galactosidase synthesis in these strains showed that the repressive effect of pts mutations was revealed in lac+, lacI, lacOc and cya bacteria, but it was lost in lacP and crp strains. It was concluded that mutational damage to the general components of the phosphoenolpyruvate-dependent phosphotransferase system diminishes activity of the lac promoter. The results obtained led to the conclusion that pts gene products (apparently phospho approximately HPr) are necessary for the initiation of transcription of catabolite-sensitive operons in E. coli.