The importance of the binding-protein-dependent Mgl system to the transport of glucose in Escherichia coli growing on low sugar concentrations.
Glucose limitation in chemostats derepressed the binding-protein-dependent Mgl transport system, which is strongly repressed during growth in batch culture with high glucose levels. The limitation-induced Mgl activity was higher than that of batch cultures "fully induced" for the Mgl system after growth on glycerol plus fucose. Mgl- strains were impaired compared to Mgl+ bacteria in removing glucose from sugar-limited chemostats and were outcompeted in mixed continuous culture on limiting glucose. The influence of Mgl was not observed on growth with limiting maltose or non-carbohydrates, and thus was specific for glucose, a known substrate of the Mgl system. In the absence of the two glucose-specific membrane components of the phosphoenolpyruvate:sugar phosphotransferase system, non-PTS-dependent growth on glucose was observed in continuous culture, but only under sugar-limited conditions derepressing the Mgl system and not in glucose-rich batches or continuous culture. Hence growth of Escherichia coli on glucose at micromolar concentrations involves a significant contribution of a binding-protein-dependent transport system. The participation of multiple transporters in glucose transport can account for the complex non-hyperbolic dependence of growth-rate on glucose concentration and for discrepancies in studies attempting to describe growth on glucose purely in terms of phosphotransferase kinetics.
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Department of Microbiology, University of Sydney, N.S.W., Australia.
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D001693:Biological Transport, Active / Q000502:physiology; D003470:Culture Media; D004926:Escherichia coli / Q000254:growth & development* / Q000378:metabolism; D005690:Galactose / Q000493:pharmacokinetics; D005947:Glucose / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D008320:Maltose / Q000493:pharmacokinetics; D008756:Methylgalactosides / Q000493:pharmacokinetics*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000378:metabolism
D003470:Culture Media; D008756:Methylgalactosides; D009004:Monosaccharide Transport Proteins; D008320:Maltose; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; D005947:Glucose; D005690:Galactose