Glucose transport in Salmonella typhimurium and Escherichia coli

We have investigated the claim by Schweiger and coworkers [Eur. J. Biochem. 102(1979)231-236] that glucose transport in Escherichia coli is catalyzed mainly by an ATP-dependent transport system instead of the phosphoenolpyruvate:sugar phosphotransferase system. A major argument was the differential effect of 2,4-dinitrophenol on glucose uptake and the transport of its non-metabolizable analogue, methyl alpha-glucoside. Whereas the first was inhibited, the second was stimulated. When subsequent glucose metabolism is prevented by introducing mutations that eliminate glucose 6-phosphate metabolism, 2,4-dinitrophenol does not inhibit glucose transport. Although dinitrophenol inhibited in wild-type cells of E. coli and Salmonella typhimurium the uptake of 14C label in cells using [U-14C]glucose as a substrate, disappearance of glucose from the medium was not affected or only slightly affected. Since uptake represents a combination of transport and subsequent metabolism, retention of labelled material depends on the balance of incorporation of label in cellular material and efflux of labelled compounds. Our experiments show that inhibition of the uptake of labelled glucose by 2,4-dinitrophenol is not due to inhibition of transport as suggested by Schweiger and coworkers, but to increased efflux of labelled compounds such as acetate and pyruvate. In addition, incorporation of label in cellular material is lowered by dinitrophenol. Inhibition of uptake by dinitrophenol is found with many labelled sugars, including mannitol, galactose and glycerol, the transport of which is energized in quite different ways. We conclude that there is no need to postulate a novel ATP-driven system for glucose transport. All results can be explained with the phosphoenolpyruvate:glucose phosphotransferase system as the main if not sole glucose transport system