Utilization of exogenous glucose-1-phosphate as a source of carbon or phosphate by Escherichia coli K12: respective roles of acid glucose-1-phosphatase, hexose-phosphate permease, phosphoglucomutase and alkaline phosphatase.
The periplasmic acid glucose-1-phosphatase (G-1-Pase) encoded by gene agp is necessary for the growth of Escherichia coli in a minimal medium containing glucose-1-phosphate (G-1-P) as the sole source of carbon. From a mutant in which the agp gene was inactivated, suppressors were isolated which recovered the ability to utilize G-1-P as carbon source. The mutants constitutively expressed hexose phosphate permease activity (encoded by uhpT). The mutation involved mapped in the uhp region and, unlike those of wild-type strains, bacteria of the suppressed strains required phosphoglucomutase (pgm), to grow on G-1-P. Surprisingly, in a minimal medium deprived of inorganic phosphate, uhpT+ bacteria lacking the two enzymes, alkaline-phosphatase (phoA) and glucose-1-phosphatase (agp), could utilize G-1-P as the sole source of phosphate, and also as both the sole phosphate and carbon source provided the integrity of pgm and of uhpT was conserved. Although glucose-6-phosphate, the inducer of UhpT permease, was not present in the medium, the activity of uhpT was greatly stimulated by inorganic phosphate depletion. This phosphate-starvation-induced bypass of G-1-Pase by UhpT + Pgm systems shows that agp is essential for G-1-P assimilation as a carbon source only in a high-phosphate medium, a result in agreement with the lack of agp regulation by inorganic phosphate.