PHOTOREACTIVATION IN THE EXTREME HALOPHILIC ARCHAEBACTERIUM Halobacterium cutirubrum

Abstract

Photoreactivation in the extreme halophilic archaebacterium Halobacterium cutirubrum was studied both in vivo and in v i m . Cells irradiated with ultraviolet (UV)-fluences up to 350 JimZ could be completely photoreactivated, indicating very efficient repair of pyrimidine dimers in UV-irradiated DNA. Dark repair is apparently absent in Halobacterium since liquid holding under non-growth conditions did not influence the survival of UV-irradiated cells, while cells remained completely photoreactivable with no change in the kinetics of photoreactivation. Experiments with Halobacterium isolates of different carotenoid content indicated that carotenoids do not influence either UV-inactivation or photoreactivation. Small differences in the rates of UV-inactivation and photoreactivation could be assigned to the occurrence of gas vesicles. Flash experiments and the temperature dependence of photoreactivation indicated an enzymatical reaction. This was confirmed by in vitro experiments with partially purified photoreactivating enzyme. The in vivo action spectrum of photoreactivation showed a main band in the 400470 nm region with a maximum at 440 nm. Comparison with action spectra of other microorganisms classified the Halobacterium enzyme as a 8-hydroxy-5-deazaflavin type photoreactivating enzyme.

Photoreactivation in an archaeon from geothermal environments

“…Streptomyces griseus photolyase, in contrast, has an 8-hydroxy-5-deazaflavin derivative; the absorbance and action spectra of this photolyase each have a single maximum near 445 nm (Jagger et al, 1970;Sancar & Sancar, 1988 (Jagger et al, 1970;Harm, 1980;Kiener et al, 1985;Eker et al, 1991). Although resolution of its precise shape is limited by scatter in the values measured, the action spectrum of photoreactivation for UV-treated S. acidocaldarius cells appears significantly broader than either of the two classical types described above.…”

“…thermoautotrophicum exhibited photoreactivation neither in vivo (Kiener et al, 1985) nor in vitro (Kiener et al, 1989), and Hb. cutirubrum exhibited only about 20 % maximal photoreactivation (Eker et al, 1991); in contrast, S. acidocaldarius has its apparent maximum near that wavelength (Fig. 5 ) .…”

“…Saccharomyces cerevisiae and Escherichia coli photolyases use a pterin derivative in this role (Sancar & Sancar, 1987) and their action spectra in vivo and in uitro have maxima near 380nm (Sancar & Sancar, 1988;Eker et al, 1991). Streptomyces griseus photolyase, in contrast, has an 8-hydroxy-5-deazaflavin derivative; the absorbance and action spectra of this photolyase each have a single maximum near 445 nm (Jagger et al, 1970;Sancar & Sancar, 1988 (Jagger et al, 1970;Harm, 1980;Kiener et al, 1985;Eker et al, 1991).…”

“…This is a function of the excision-repair system, which does not require visible light. One of the classical manifestations of excisionrepair of pyrimidine dimers, known as 'liquid holding recovery', is an increase in the viability of nongrowing cell suspensions incubated in the dark (Harm, 1980;Fitt et al, 1983;Eker et al, 1991). The halophilic archaeon Hb.…”

Photoreactivation in Airborne Mycobacterium parafortuitum

“…The welldocumented magnitudes of PR observed in UV-inactivated waterborne bacteria suggest that PR may adversely influence the performance of UV bioaerosol irradiation systems. PR studies of bacteria suspended in liquid or distributed on agar plate surfaces have empirically identified the degree of UVinduced damage (22) and the length of exposure to photoreactivating light (8,21) as factors that affect the extent of PR. An inverse relationship between UV dose and the extent of PR has been observed for wastewater coliforms (22) and the bacterium Haemophilus influenzae (52).…”