Escherichia coli glycogen metabolism is controlled by the PhoP-PhoQ regulatory system at submillimolar environmental Mg2+ concentrations, and is highly interconnected with a wide variety of cellular processes

Abstract

Using the Keio collection of gene-disrupted mutants of Escherichia coli, we have recently carried out a genome-wide screening of the genes affecting glycogen metabolism. Among the mutants identified in the study, Delta mgtA, Delta phoP and Delta phoQ cells, all lacking genes that are induced under low extracellular Mg2+ conditions, displayed glycogen-deficient phenotypes. In this work we show that these mutants accumulated normal glycogen levels when the culture medium was supplemented with submillimolar Mg2+ concentrations. Expression analyses conducted in wild-type, Delta phoP and Delta phoQ cells showed that the glgCAP operon is under PhoP-PhoQ control in the submillimolar Mg2+ concentration range. Subsequent screening of the Keio collection under non-limiting Mg2+ allowed the identification of 183 knock-out mutants with altered glycogen levels. The stringent and general stress responses, end-turnover of tRNA, intracellular AMP levels, and metabolism of amino acids, iron, carbon and sulfur were major determinants of glycogen levels. glgC::lacZY expression analyses using mutants representing different functional categories revealed that the glgCAP operon belongs to the RelA regulon. We propose an integrated metabolic model wherein glycogen metabolism is (a) tightly controlled by the energy and nutritional status of the cell and (b) finely regulated by changes in environmental Mg2+ occurring at the submillimolar concentration range.

Glycogen is the primary source of glucose during the lag phase of E. coli proliferation

“…Recently, the property of glycogen has been extensively investigated [20]. E. coli mutants deleted in either pts or pgm genes display glycogenless phenotypes, and these genes showed nonessential for cell growth [18,22].…”

“…This indicates that after 8 hr, glucose uptake is not mainly used for cell proliferation, and there should be another destination for these sugar groups. We should not forget that there is another pathway connected with G6P, glycogen metabolism pathway [18,21,22], which is an intracellular sugar storage mechanism. This suggests that, in this phase, glucose is changed to glycogen.…”

“…Numerous studies focused on glycogen storage diseases in human [10][11][12][13][14][15][16]. There are also many studies on glycogen network in prokaryotes [17][18][19][20][21][22][23][24][25], which serve as simple models of glycogen storage diseases in mammals, but most of them focus on glycogen network only. On the other hand, in the area of metabolic engineering, the most studied carbohydrate metabolic pathways are EMD (the Embden-Meyerhof-Parnas pathway), PPP and ED (the Entner-Doudoroff pathway) [26], but seldom glycogen network was taken into account in biological or computational central metabolism models [27][28][29][30][31][32][33][34][35].…”

Role of Maltose Enzymes in Glycogen Synthesis by Escherichia coli

“…It involves the global carbon storage regulator CsrA (2,53), the cyclic AMP (cAMP)/catabolite gene activator protein (CAP) system (39), and the stringent response (38). In addition, the two-component regulatory system PhoP-PhoQ (29) connects the system to Mg 2ϩ levels, and even the phosphotransferase system appears to affect the glycogen phosphorylase involved in the degradation of glycogen (42,43). glgS, an additional gene involved in glycogen synthesis, is not part of the glg gene cluster.…”

Reaction Kinetics of Substrate Transglycosylation Catalyzed by TreX of Sulfolobus solfataricus and Effects on Glycogen Breakdown

“…Glycogen metabolism is highly interconnected with a wide variety of cellular processes, including stringent response, Mg 2ϩ availability, and osmotic pressure (40). Therefore, glycogen as a reserve macromolecule has little effect on the internal osmotic pressure of the cell (2).…”