Promoted proliferation of an SOD-deficient mutant of Escherichia coli under oxidative stress induced by photoexcited TiO2

Abstract

An SOD null mutant of Escherichia coli (IM303) and its wild-type strain (MM294) were cultivated with or without sublethal oxidative stress generated from photoexcited TiO2. Concerning maximum specific growth rate of the cells, mum, measured under various conditions, the mum value of IM303 cells increased notably in the presence of TiO2 illuminated with light (I = 12.5 W m(-2)), being about two times higher than that of the cells grown in the absence of TiO2 and light. The mum value of IM303 cells under the oxidative condition restored to a level comparable to that of wild-type MM294 cells, which coincided with the finding that the content of reactive oxygen species lowered in IM303 cells under the oxidative stress. Colony isolation was conducted to obtain the cells prevailing in the early culture phase of IM303 cells in the presence of TiO2 and light. It was found that the isolates exhibited the outgrowing properties with the increased mum values under both the conditions with and without TiO2 and light. It was also indicated that in the culture of typically selected isolate, the cells started to grow with a relatively short lag in a threonine-minus medium.

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

“…In our previous study (Kim et al 2004), it was found that SOD-deficient E. coli cells suffering sublethal oxidative stress from photoexcited titanium dioxide (TiO 2 ) unexpectedly exhibited stimulated growth and decreased ROS content in the cells, suggesting that some changes of metabolic patterns occur to cope with the stress. In the present work, the SOD-deficient cells were cultivated under the conditions with and without photoexcited TiO 2 , and physiological responses were compared in terms of mRNA expressions and activities of enzymes in acetic acid-producing pathway and TCA cycle, to understand a strategy of the cells for surviving under the oxidative stress.…”

The Gene yggE Functions in Restoring Physiological Defects of Escherichia coli Cultivated under Oxidative Stress Conditions

“…In our previous work (12), it was reported that the population of SOD-deficient mutant of E. coli IM303 contained a trace of spontaneously derived variant cells which prevailed during the culture under the oxidative stress generated by photoexcited titanium dioxide (TiO 2 ). This result suggested that the variant cells possibly acquired a certain defense system against the oxidative stress besides the SOD mechanism.…”

“…Strain IM303 (I4) was one of isolates obtained from an original population of the mutant (12 (21). RNA extraction was conducted as follows, using IM303 (I4) cultures with and without the oxidative stress generated by light-irradiated TiO 2 .…”

“…ROS content in the cells was quantified with 5-(and-6)-chloromethyl-2Ј,7Ј-dichlorofluorescin diacetate (C-6827; Molecular Probes Inc., Eugene, OR) and was expressed on an H 2 O 2 equivalent basis, as described elsewhere (12).…”

“…Previous work described that the original population of SOD null mutant of E. coli, IM303, contained a trace of spontaneously derived variant cells, and these variant cells were permitted to survive and prevail during the culture with the sublethal oxidative stress generated from light-irradiated TiO 2 (12). As shown in Fig.…”