Heat-shock-increased survival to far-UV radiation in Escherichia coli is wavelength dependent

Exposure of Escherichia coli to intestinal myoelectrical activity-related electric field induces resistance against subsequent UV(254 nm) (UVC) irradiation

Survival of Escherichia coli K-12 AB1157 irradiated with UVC (UV(254 nm)) was enhanced after pre-treatment with a low-tension electric field (EF). The EF used was identical to the electrical field generated by the small intestine (myoelectrical migrating complex--MMC), registered in a healthy calf and transmitted into the memory of an EF generator. The EF emitted by the generator was transmitted via electrodes placed in shaken bacterial cultures. The protective effects of the EF on the E. coli survival after exposure to UV were: (i) observed only for the dnaJ(+)dnaK(+) strain, and not for the DeltadnaJdnaK heat shock mutant; (ii) strictly dependent on the temperature at which the bacteria were grown; (iii) most obvious when the bacteria were incubated at 37 degrees C. Moreover, the MMC-related EF and a higher temperature (40 degrees C) show a similar protective effect against UV-irradiation. The results point to the involvement of the heat shock response in the low-tension EF-induced protection of bacterial cells against UVC-irradiation. Additionally, treatment with the MMC-related EF affects total protein contents and their pattern in E. coli cells. The EF-treatment did not show any influence on the level of the argE3(ochre) --> Arg(+) reversions.

Non-coherent visible and infrared radiation increase survival to UV (254 nm) in Escherichia coli K12

Interactions between visible or infrared (IR) and ultraviolet (UV, 254 nm) radiation have been studied in E. coli. Pre-illumination with non-coherent monochromatic 446, 466, 570 and 685 nm radiation, as well as with polychromatic red and IR radiation at room temperature, leads to increased cell survival after a subsequent irradiation with UV light. In the thermic range of the spectrum (red and IR), IR but not red light pre-treatment is able to increase cell survival to a subsequent lethal heat (51 degrees C) challenge, suggesting that increased UV survival may be due to IR-induced heat-shock response. On the other hand, visible-light-induced resistance may be due to a different mechanism, possibly involved with unknown bacterial light receptors.

A non-excision uvr-dependent DNA repair pathway of Escherichia coli (involvement of stress proteins)

In UV-irradiated excision-proficient (uvr+) Escherichia coli, pre-induced by simultaneous pre-starvation for thymine (T) and amino acids (AAs), and/or a low UV pre-dose applied after prestarvation for AAs, pyrimidine dimer excision (PDE) is reduced without an adequate increase of UV sensitivity and UV mutagenesis. The unexcised lesions are tolerated by a putative repair pathway that is uvr dependent but does not involve excision. The process consists of PDE inhibition, which requires outer membrane protease OmpT, and subsequent pyrimidine dimer (PD) toleration, which may be mediated by interaction with a sister duplex using a number of SOS and stress-inducible proteins.

The pre-UV nutritional stresses increase UV resistance, decrease UV mutagenesis and inhibit excision repair

Nutritional stresses applied to E. coli prior to UV irradiation increase UV resistance and decrease UV mutagenesis. This effect is uvrA-dependent and might reflect a more efficient excision of pyrimidine dimers [1]. The data presented here, however, indicate that after prestarvation for glucose or amino acids pyrimidine dimer excision (PDE) was partly inhibited. It appears that the stress conditions stimulate a mode of uvr-dependent tolerance of lesions, efficient and precise. Possible modes of PDE inhibition and lesion tolerance are discussed.

Stress proteins in the cellular response to ultraviolet radiation

Virtually all cells-from prokaryotes to highly differentiated mammalian tissues-respond to a sudden increase in temperature with increased production of a limited set of proteins, called heat shock proteins or stress proteins (hsp). Other stress factors such as alcohol, heavy metals, oxidants and agents leading to protein denaturation are equally able to induce a similar response. Induction of hsp is followed by a transient state of increased resistance to further stress. Many hsp function as "molecular chaperones" by binding to partially folded or misfolded proteins thus preventing their irreversible denaturation during stress exposure. The high evolutionary conservation of this reaction suggests its importance for the survival of cells and tissues under hostile environment conditions. Ultraviolet radiation (UV) exerts many potentially harmful effects on prokaryotic and eukaryotic cells and hsp may help the cell to cope with UV-induced damage. This review will focus on the role of hsp in the cellular response of mammalian skin to UV. Hsp have been detected in resting as well as stress exposed epidermal and dermal cells and experimental evidence points to the fact that these proteins mediate protection from UV induced cell death in vitro and in vivo. Experimental studies further indicate that UV itself might be able to induce the expression of specific hsp. Thus, hsp might provide an adaptive cellular response to increasing exposure to UV. Furthermore, UV-activation of hsp synthesis may provide a valuable model for investigation of the transcription regulation of UV-induced gene expression.