Occurrence of carbon catabolite repression-regulated mechanism involved in the transport of extracellular ADP-glucose in Escherichia coli

Abstract

ADP-glucose is the precursor molecule for glycogen and starch biosynthesis in bacteria and plants, respectively. Due to the high abundance of this nucleotide-sugar in tubers and endosperms present in the normal diet of many animals, we explored the possible occurrence of an ADP-glucose transport system in the enterobacterial species Escherichia coli. To avoid artifacts resulting from the possible conversion of periplasmic ADP-glucose breakdown products into glycogen, in this work we used glglC and pgm null mutants unable to catalyze the reversible conversion of ADP-glucose into glucose-1-P, and glucose-1-P into glucose-6-phosphate, respectively. Noteworthy, these cells converted the exogenoulsy added ADP-glucose into glycogen. Uptake of ADP-glucose was confirmed by the disappearance of this nucleotide-sugar from the culture medium. ΔpgmΔptsG, ΔpgmΔptsH, ΔpgmΔptsI and ΔpgmΔcrr cells impaired in the PTS components produced glycogen from exogenously added ADP-glucose, indicating that the transport of this nucleotide-sugar is not mediated by PTS. Furthermore, ΔpgmΔcyaA and ΔpgmΔcrp cells, both impaired in the CRP-cAMP carbon catabolite repression mechanism, neither incorporated ADP-glucose nor produced glycogen from ADP-glucose, demonstrating that the uptake of this nucleotide-sugar is CRP-cAMP regulated in E. coli. Finally, using a systematic and comprehensive gene-disrupted mutant collection of E. coli we identifi ed some genes belonging to the CRP-cAMP regulon encoding membrane proteins whose absence impair ADP-glucose transport.