Glucose Transport in Escherichia coli Mutant Strains with Defects in Sugar Transport Systems

Abstract

In Escherichia coli, several systems are known to transport glucose into the cytoplasm. The main glucose uptake system under batch conditions is the glucose phosphoenolpyruvate:carbohydrate phosphotransferase system (glucose PTS), but the mannose PTS and the galactose and maltose transporters also can translocate glucose. Mutant strains which lack the enzyme IIBC (EIIBC) protein of the glucose PTS have been investigated previously because their lower rate of acetate formation offers advantages in industrial applications. Nevertheless, a systematic study to analyze the impact of the different glucose uptake systems has not been undertaken. Specifically, how the bacteria cope with the deletion of the major glucose uptake system and which alternative transporters react to compensate for this deficit have not been studied in detail. Therefore, a series of mutant strains were analyzed in aerobic and anaerobic batch cultures, as well as glucose-limited continuous cultivations. Deletion of EIIBC disturbs glucose transport severely in batch cultures; cyclic AMP (cAMP)-cAMP receptor protein (CRP) levels rise, and induction of the mgl operon occurs. Nevertheless, Mgl activity is not essential for growth of these mutants, since deletion of this transporter did not affect the growth rate; the activities of the remaining transporters seem to be sufficient. Under conditions of glucose limitation, mgl is upregulated 23-fold compared to levels for growth under glucose excess. Despite the strong induction of mgl upon glucose limitation, deletion of this transport system did not lead to further changes. Although the galactose transporters are often regarded as important for glucose uptake at micromolar concentrations, the glucose as well as mannose PTS might be sufficient for growth at this relatively low dilution rate.T he transport of carbon sources, especially glucose, is an important field of research that has been previously investigated in Escherichia coli. The main uptake system under conditions of glucose excess is the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). It plays an important role not only in the transport and phosphorylation of carbon sources but also in the regulation of carbon metabolism and chemotaxis (for an overview, see reviews in references 11a, 47a, 50, and 50a). Glucose transport into the cytoplasm by EIICB Glc (encoded by ptsG) is coupled to its phosphorylation. The phosphate group is derived from phosphoenolpyruvate (PEP) and is transferred via a cascade of proteins, enzyme I (EI), HPr, EIIA, and EIIB. EI and HPr are general PTS proteins, while the EII proteins are carbohydrate specific. Like the glucose PTS, the mannose PTS (encoded by manXYZ) has been shown to play a role in transportation and phosphorylation of glucose under aerobic conditions with glucose as the sole carbon source (26), although PtsM has a lower affinity for glucose than PtsG (K m PtsM , 1.3 mM [9]; K m PtsG , 10 to 20 M [26]). Besides the phosphotransferase systems, the galactose transport systems, the galact...

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Arginine Functionally Improves Clinically Relevant Human Galactose-1-Phosphate Uridylyltransferase (GALT) Variants Expressed in a Prokaryotic Model

“…For non-transformed E. coli DgalT cultured under glucose or glucose plus galactose, the growth curves were indistinguishable, since glucose is the preferred carbon source and galactose represents no toxicity in the presence of this hexose. This absent toxicity of galactose likely results from carbon catabolite repression exerted by glucose, which represses the galactose uptake systems GalP and Mgl (G€ orke and St€ ulke 2008; Misko et al 1987;Shimizu 2013;Steinsiek and Bettenbrock 2012). In the presence of glycerol, transported into E. coli through facilitated diffusion (Chu et al 2002), the growth rate was approximately half of that observed in the presence of glucose, confirming that this polyol is not as efficient as glucose as a carbon source, as previously described (Chu et al 2002).…”

Reduction of translating ribosomes enables Escherichia coli to maintain elongation rates during slow growth

“…The strains used in this study are either wild type E. coli NCM3722 strain 51,52 or its derivatives: NQ1261 (Δ ptsG , deleted of the gene encoding the main glucose transporter PtsG), which grows slowly in glucose medium 53 , NQ1468 used for measuring LacZα induction kinetics, and the WE2015 series of strains used for measuring the translational elongation rate of various proteins using the hybrid LacZα approach described below. E. coli MG1655 strain used in the ribo-seq study of Li et al 3 was also obtained directly from G. W. Li.…”