Metabolic alternations in SOD-deficient Escherichia coli cells when cultivated under oxidative stress from photoexcited titanium dioxide.

Superoxide dismutase (SOD)-deficient Escherichia coli was cultivated under the oxidative stress generated by photoexcited titanium dioxide. These cells showed higher growth rate and glucose consumption rate with accelerated accumulation of acetic acid in the medium, compared to the cells cultivated under the normal condition without the stress. Under the stress condition, the activity of acetate kinase and mRNA expressions of the enzymes for acetic acid production (pta and ackA) were approximately doubled, while the activity of citrate synthase and mRNA expressions of the enzymes in TCA cycle (gltA, acnA, icd, sucA, sucC, sdhA, fumA and mdh) were repressed by about half, as compared with those under the normal condition. These results suggest that the stress-suffering cells switch the metabolic pathway into a "suppressed aerobiosis", possibly for lowering the generation of reactive oxygen species.