The metabolism of gluconate in Escherichia coli. The subsidiary system and the nature of the gntS gene

The transport and phosphorylation of gluconate in E. coli occurs through two systems (GntI and GntII) which duplicate activities. bioH-asd deletion mutants do not grow on media with gluconate as sole carbon source because they lack the GntI system and do not express GntII. Although E. coli C177 is a Delta(bioH-asd) mutant, it carries the pyrB Linked mutation gnt177 that enables it to metabolize this substrate through inducible expression of the GntII system. Several gntS derivatives which are unable to grow on gluconate were isolated from E. coli C177 by spontaneous curing of the transposon Tn10 previously inserted at the gntS locus (zif::Tn10, min 95.3). A representative gntS mutant, E. coli TI141A retained the ability to take up gluconate but had lost the thermosensitive gluconokinase activity (gene gntV, min 96.9). Furthermore, it could be demonstrated that gntV is repressed in E. coli TI141A. The results indicate that gntS might specify a trans-acting positive regulator involved in the control of at least the expression of the thermosensitive gluconokinase (GntII), instead of a gluconate uptake system as it was previously postulated. Likewise, these results can be used to reconsider whether the locus altered by the gnt177 lesion is allelic with that of the GntII permease instead of a regulator, as it was originally postulated.