Activation of glucose transport under oxidative stress in Escherichia coli

Global transcription studies have identified a large number of redox-responsive genes, although the biological relevance of this regulation has not been experimentally tested. In particular, several genes coding for enzymes involved in glucose metabolism have been identified as redox-responsive in Escherichia coli. However, only zwf, which codes for glucose-6-phosphate dehydrogenase, has been shown experimentally to affect the cellular resistance to oxidative stress. We addressed the question of whether ptsG, coding for the membrane component of the glucose-specific transporter system, and pgi, coding for phosphoglucose isomerase, two additional genes identified in whole-genome functional screens, are indeed relevant in antioxidant defense. PTS assays showed that glucose transport was induced under oxidative stress elicited by the superoxide-producing agent paraquat (PQ). This induction of glucose transport under oxidative stress was dependent on the soxRS genes, coding for a sensor- transcriptional activator system, and ptsG. The binding of purified SoxS to the ptsG promoter region was shown by gel mobility-shift assay, and the activation of the ptsG promoter P1 was demonstrated by primer extension assays. Finally, a ptsG mutant strain was hypersensitive to PQ when grown in rich medium plus glucose, but not in rich medium without glucose. The pgi gene showed the same pattern of regulation by oxidative stress under the control of the SoxRS system, and a strain carrying a pgi deletion was hypersensitive to PQ.