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Biological UV dosimeters in simulated space conditions
Advances in Space Research 33 (2004) 1302–1305 www.elsevier.com/locate/asr
Biological UV dosimeters in simulated space conditions Gy. Ronto
a,b,*
f a, H. Lammer , A. Berces b, A. Fekete a, G. Kov acs b, P. Gro
c
a
c
Institute of Biophysics and Radiation Biology, Faculty of Medicine, Semmelweis University, P.O.B. 263, Budapest H-1444, Hungary b MTA-SE Research Group for Biophysics, Hungarian Academy of Sciences, P.O.B. 263, Budapest H-1444, Hungary Department of Extraterrestrial Physics, Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, Graz A-8042, Austria Received 20 January 2003; received in revised form 4 April 2003; accepted 30 July 2003
Abstract Polycrystalline uracil thin layers participate in the phage and uracil response (PUR) experiment, assigned to the biological dosimetry of the extraterrestrial solar radiation on the International Space Station (ISS). In ground based experiments (experiment verification tests), the following space parameters were simulated and studied: temperature, vacuum and short wavelength UV (UVC, down to 200 nm) radiation. The closed uracil samples proved to be vacuum-tight for 7 days. In the tested temperature range (from )20 to +40 C) the uracil samples are stable. The kinetic of dimer formation (dimerization) and reversion (monomerization) of uracil dimers due to short wavelength UV radiation was detected, the monomerization efficiency of the polychromatic deuterium lamp is higher than that of the germicidal lamp. A mathematical model describing the kinetic of monomerization–dimerization was constructed. Under the influence of UV radiation the dimerization–monomerization reactions occur simultaneously, thus the additivity law of the effect of the various wavelengths is not applicable. 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Astrobiology; Biological UV dosimeters; Simulated space conditions
1. Introduction The European Space Agency (ESA) supports research programs in exo/astrobiology providing exposure platforms for biological experiments in various space missions. Response of Organisms to Space Environment (ROSE) an international scientific consortium was set up aiming to investigate outside the International Space Station (ISS), i.e. in EarthÕs orbit the hostile space environment for the microorganisms and molecules having essential role in life (Horneck et al., 1999). The parameters, characteristic for the space environment, are the temperature (low and high), space vacuum, galactic cosmic radiation and solar radiation. The latter is hazardous because of the high irradiance and unusual spectral composition (Weber and Greenberg, 1985; Rettberg and Rotschild, 2002). Phage and uracil response (PUR) is one of the experiments of the ROSE consortium. The main goal of the PUR experiment is the *
Corresponding author. Tel.: +36-1-267-6261; fax: +36-1-266-6656. E-mail address: [email protected] (Gy. Ronto).
investigation and quantification of the effect of specific space parameters on the survivability of nucleic acids/of their models: bacteriophage T7, isolated phage T7 nucleic acid, polycrystalline uracil. Phage T7 and uracil were used for solar UV dosimetry purposes on the EarthÕs surface (Ront o et al., 1992; Gr of et al., 1996). Our aim is to study how to adapt the concepts and technologies of biological UV dosimetry to the space conditions. Recently, the effect of short wavelength UV components of the solar radiation on these objects was studied theoretically (Ront o et al., 2002) on bacteriophage T7, while this paper presents the results of the experiment verification tests (EVTs) performed on polycrystalline uracil. Some of the EVT results obtained on bacteriophage T7 and isolated phage DNA are published in this issue (Fekete et al., 2004).
2. Methods The space parameters simulation facilities, available for EVT purposes, are summarized in Table 1.
0273-1177/$30 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2003.07.051
Gy. Ronto et al. / Advances in Space Research 33 (2004) 1302–1305
1303
Table 1 Facilities used in simulation experiments Institution, location
Project name
Principal investigator
Studied parameter
MTA-SE Research Group for Biophysics, HAS, Hungary German Aerospace Medicine, K€ oln, Germany Institute of Space Research, Graz, Austria
PRODEX
G. Ront o
Short wavelength UV
EVT, SSIOUX
G. Horneck, E. Rabbow
Temperature, vacuum
Austrian–Hungarian Scientific Cooperation
H. Lammer, N.I. K€ omle, G. Kargl
Vacuum, short wavelength UV radiation
The polycrystalline uracil thin layers were prepared according to the evaporation technique and the quality of the thin layers was controlled spectroscopically (Gr of et al., 1996; Kerekgy art o et al., 1997). The thickness of the thin layer was optimized for 70 nm. Fig. 1 presents the cross section of the so called sandwich forms of uracil samples: the thin layers are under a vacuumtightly closed fluoride window and an inert gas can be enclosed into the inner volume. Irradiations were performed with low pressure mercury lamp (Tungsram, germicidal lamp; 15 W) and 300 W deuterium lamp (Oriel). The former has a strong characteristic line at k ¼ 254 nm, while the latter is a polychromatic source with a continuous spectrum from 400 down to 200 nm (in atmospheric conditions). The administered UV dose was measured with Polytec AN/ S10 radiometer. Under the influence of UV-B, UV-C irradiation at normal temperature and atmospheric conditions photoproducts (mainly cyclobutane dimers, 6–4 adducts) are formed (Fisher and Johns, 1976; Rosenstein and Mitchell, 1987; Fekete et al., 1998), this effect can be measured by the extent of the decrease of the characteristic absorption (at 280 nm) of uracil (Gr of et al., 1996). For irradiations with germicidal and deuterium lamps dose–effect curves were determined. The effect was expressed as the change of the optical density (OD) value of the irradiated uracil thin layer at the wavelength of 280 nm. The OD value of the uracil samples depends on the thickness of the layer, thus the starting OD values (without irradiation) were standardized by the preparation of the layers. For comparison the starting OD-value was adjusted to 0.45.
3. Results and discussion 3.1. Effect of vacuum The samples were exposed to vacuum in sandwich form with vacuum tightly closed measuring cell at room temperature. Applying either 103 Pa (Graz) or 1.7 104 Pa (K€ oln) for 48 h or 7 days, respectively, no significant change has been detected in the traditional UV spectra of the samples. This result indicates the safe closing of the sandwich samples, however, without covering at room temperature the characteristic absorption spectrum of the uracil disappears indicating the complete evaporation of the substance. 3.2. Effect of temperature The effect of the temperature was tested by incubation of the samples for 7 days at +40 C (DLR, K€ oln). Based on the absorption spectrum of the samples this temperature did not cause any change in the structure of the polycrystalline uracil layer. Taking into account our results obtained earlier with low (down to )20 C) temperature, one can state that the polycrystalline uracil at least in the range from )20 to +40 C is insensitive. Investigation in a broader temperature range as well as the study of the tolerance for the large scale temperature variations that might occur during the flight, will be done in the future in the frame of the EXPOSE-EVT experiment. 3.3. Effect of UV radiation
Fig. 1. Cross section of the uracil samples.
UV exposure of the samples causes a decrease of the OD value (absorbance), indicating the decrease of the intact form of uracil molecules in the thin layer, in other words the extent of the decrease of OD value shows the extent of the photoproduct formation in nucleic acid/in uracil model. Fig. 2(a) shows the decrease of the OD of uracil layers under the influence of the UV irradiation from germicidal lamp, while Fig. 2(b) does the same under the irradiation with deuterium lamp. Both dose–effect curves
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Gy. Ronto et al. / Advances in Space Research 33 (2004) 1302–1305
Fig. 2. Decrease of the OD value of uracil thin layer in dependence of UV doses from germicidal (a) and deuterium lamp (b).
having identical starting OD values, show a tendency for saturation, however, the saturation levels differ in the two cases. With germicidal lamp the saturation exists at a lower OD value than with deuterium lamp (at about 60% and 80% of the original OD values, respectively). In Bacillus subtilis spores after exposure to germicidal lamp and to extraterrestrial solar radiation Horneck et al. (1984) demonstrated spore photoproducts (5-thyminyl-5,6-dihydrothymine) and two other products. According to our results the short wavelength UV radiation (UV-B and UV-C), specifically in polycrystalline uracil layers, prefers the formation of cyclobutane dimers (Fidy and Raksanyi, 1978; Gr of et al., 1996; Fekete et al., 1998). In the irradiated uracil sample the lower OD value corresponds to a larger number of photoproducts (in this case photodimers) induced by the irradiation with germicidal lamp, thus the saturation level in Fig. 2(a) corresponds to a higher amount of dimers, than in Fig. 2(b). The presence of the saturation level in the exposed uracil layer in both cases can be interpreted by two simultaneous photoreactions occurring in opposite directions: the photons can either induce the addition of two uracil bases (photoaddition or photodimerization) or can break the dimers into two uracil molecules (monomerization or photoreversion). Both effects were described earlier (e.g. Fisher and Johns, 1976) and were found also in simple biological models (Ront o et al., 1967). The difference between the two saturation levels in Figs. 2(a) and (b) reflect the different levels of the
equilibrium between dimer formation and monomerization. In other words: the shorter wavelength components of deuterium lampÕs spectrum are more efficient in the monomerization reaction of the uracil photoproducts than germicidal lamp, thus the equilibrium occurs at a lower number of dimers. Aiming to study this effect after the previous irradiation with germicidal lamp to saturation, the thin layers were exposed by deuterium lamp. Fig. 3(a). demonstrates the effect: the OD value, characteristic for the germicidal lamp irradiation, increased approximately up to the saturation level obtained with deuterium lamp according to the Fig. 2(b). A second exposure of the samples with germicidal lamp, irradiated former to saturation with deuterium lamp, causes a further decrease of the OD value (Fig. 3(b)). A kinetic model was developed to describe the dose– effect relationship of the monomerization–dimerization reaction induced by the exposure with a constant irradiance dnm ¼ kMD nm þ kDM nd ; dt
ð1Þ
where nm and nd denote the number of monomers and dimers at time t, while kMD and kDM are the rate constants of dimerization and monomerization, respectively. The number of monomers at the time t ¼ 0 can be given as nm ðt ¼ 0Þ ¼ n0m . In a layer containing at the beginning of the irradiation only monomers, the number of monomers can be written at irradiation time t as
Fig. 3. (a) Increase of the OD of UV irradiated uracil thin layer with deuterium lamp. (b) Further decrease of the OD of UV irradiated uracil thin layer with germicidal lamp.
Gy. Ronto et al. / Advances in Space Research 33 (2004) 1302–1305
nm ¼
n0m ½kDM þ kMD eðkMD þkDM Þt : kMD þ kDM
ð2Þ
The initial slope and the saturation level of the dose– effect curves both in Figs. 3(a) and (b) depend on the monomerization and dimerization rate constants and both of them depend on the spectral composition of the UV source. Determination of the wavelength dependence of the rate constants will result in the separate action spectra of monomerization and dimerization is in progress.
4. Conclusions • Uracil dimers in polycrystalline thin layers can be produced by short wavelength irradiation (UV-C) with either germicidal or deuterium lamp, that are detected with spectroscopic methods. • A proportion of the dimers induced with germicidal lamp can be reverted by irradiation with deuterium lamp having shorter wavelength components in emission spectrum. • Using polychromatic source of shorter wavelength (<280 nm) UV radiation, the additive nature (Sutherland, 2002) of the photobiological effect of the different wavelengths is not applicable, thus the modification of the biological UV dosimetry concept and method elaborated for the terrestrial solar radiation should be reconsidered in the use for extraterrestrial dosimetry. • The effect of photoreversion due to short wavelength UV components of the extraterrestrial solar radiation can contribute to the protection of life in the harsh space environment.
Acknowledgements Gy. Ront o, A. Berces, A. Fekete, G. Kov acs and H. € Lammer thank the Osterreichischer Akademischer € Austauschdienst (OAD) for supporting this work as part € of the Austrian–Hungarian OAD-project A-20/2000.
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References Fekete, A., Ront o, Gy., Heged€ us, M., M odos, K., Berces, A., Kovacs, G., Lammer, H., Panitz, C., Simulation experiments of the space environment on bacteriophage and DNA thin films. Adv. Space Res., 2004, in press. Fekete, A., Vink, A.A., Gaspar, S., Berces, A., M odos, K., Ront o, G., Roza, L. Assessement of the effects of various UV sources on inactivation and photoproduct induction in phage T7 dosimeter. Photochem. Photobiol. 68, 527–531, 1998. Fidy, J., Raksanyi, K. Spectroscopic and kinetic study of UV photochemistry of uracil thin layers. Studia Biophys. 71, 137– 138, 1978. Fisher, G.J., Johns, H.E. Pyrimidine photodimers, in: Wang, S. (Ed.), Photochemistry and Photobiology of Nucleic Acids, vol. 1. Academic Press, New York, pp. 225–294, 1976. Gr of, P., Gaspar, S., Ront o, Gy. Use of uracil thin layer for measuring biologiocally effective UV dose. Photochem. Photobiol. 64, 800– 806, 1996. Horneck, G., B€ ucker, H., Reitz, G., Requardt, H., Doose, K., Martens, K.D. Microorganisms in the space environment. Science 225, 226–228, 1984. Horneck, G., Wynn-Williams, D.D., Mancinelli, R.L., Cadet, J., Munakata, N., Ront o, G., Edwards, H.G.M., Hock, B., W€anke, H., Reitz, G., Dachev, T., H€ader, D.P., Brioullet, C., Biological experiments on the EXPOSE facility of the International Space Station, in: Proceedings of the Second European Symposium on the Utilization of the ISS, vol. ESA SP-433, pp. 459–468, 1999. Kerekgyart o, T., Gr of, P., Ront o, G. Production and basic application of uracil Dosimeters for measuring the biologically effective UV dose. Centr. Eur. J. Occup. Environ. Med. 3, 143–152, 1997. Rettberg, P., Rotschild, L. Ultraviolet radiation in planetary atmospheres and biological implications, in: Horneck, G., BaumstarkKahn, C. (Eds.), Astrobiology. Springer, Berlin, pp. 233–243, 2002. Ront o, G., Sarkadi, K., Tarjan, I. Zur analyse der UV dosiswirkungskurven der T7 bakteriophagen. Strahlentherapie 134, 151–157, 1967. Ront o, G., Gapar, S., Berces, A. Phage T7 in biological UV dose measurement. J. Photochem. Photobiol. B 12, 285–294, 1992. Ront o, G., Gaspar, S., Fekete, A., Kerekgyart o, T., Berces, A., Gr of, P. Stability of nucleic acid under the effect of UV radiation. Adv. Space Res. 30, 1533–1538, 2002. Rosenstein, B.S., Mitchell, D.L. Action spectra for the induction of pyrimidine (6–4) pyrimidone photoproducts and cyclobutane pyrimidine dimers in normal human skin fibroblasts. Photochem. Photobiol. 45, 775–780, 1987. Sutherland, J.C. Biological effects of polychromatic light. Photochem. Photobiol. 76, 164–170, 2002. Weber, P., Greenberg, J.M. Can spores survive in interstellar space? Nature 316, 403–407, 1985.
Biological UV dosimeters in simulated space conditions Gy. Ronto
a,b,*
f a, H. Lammer , A. Berces b, A. Fekete a, G. Kov acs b, P. Gro
c
a
c
Institute of Biophysics and Radiation Biology, Faculty of Medicine, Semmelweis University, P.O.B. 263, Budapest H-1444, Hungary b MTA-SE Research Group for Biophysics, Hungarian Academy of Sciences, P.O.B. 263, Budapest H-1444, Hungary Department of Extraterrestrial Physics, Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, Graz A-8042, Austria Received 20 January 2003; received in revised form 4 April 2003; accepted 30 July 2003
Abstract Polycrystalline uracil thin layers participate in the phage and uracil response (PUR) experiment, assigned to the biological dosimetry of the extraterrestrial solar radiation on the International Space Station (ISS). In ground based experiments (experiment verification tests), the following space parameters were simulated and studied: temperature, vacuum and short wavelength UV (UVC, down to 200 nm) radiation. The closed uracil samples proved to be vacuum-tight for 7 days. In the tested temperature range (from )20 to +40 C) the uracil samples are stable. The kinetic of dimer formation (dimerization) and reversion (monomerization) of uracil dimers due to short wavelength UV radiation was detected, the monomerization efficiency of the polychromatic deuterium lamp is higher than that of the germicidal lamp. A mathematical model describing the kinetic of monomerization–dimerization was constructed. Under the influence of UV radiation the dimerization–monomerization reactions occur simultaneously, thus the additivity law of the effect of the various wavelengths is not applicable. 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Astrobiology; Biological UV dosimeters; Simulated space conditions
1. Introduction The European Space Agency (ESA) supports research programs in exo/astrobiology providing exposure platforms for biological experiments in various space missions. Response of Organisms to Space Environment (ROSE) an international scientific consortium was set up aiming to investigate outside the International Space Station (ISS), i.e. in EarthÕs orbit the hostile space environment for the microorganisms and molecules having essential role in life (Horneck et al., 1999). The parameters, characteristic for the space environment, are the temperature (low and high), space vacuum, galactic cosmic radiation and solar radiation. The latter is hazardous because of the high irradiance and unusual spectral composition (Weber and Greenberg, 1985; Rettberg and Rotschild, 2002). Phage and uracil response (PUR) is one of the experiments of the ROSE consortium. The main goal of the PUR experiment is the *
Corresponding author. Tel.: +36-1-267-6261; fax: +36-1-266-6656. E-mail address: [email protected] (Gy. Ronto).
investigation and quantification of the effect of specific space parameters on the survivability of nucleic acids/of their models: bacteriophage T7, isolated phage T7 nucleic acid, polycrystalline uracil. Phage T7 and uracil were used for solar UV dosimetry purposes on the EarthÕs surface (Ront o et al., 1992; Gr of et al., 1996). Our aim is to study how to adapt the concepts and technologies of biological UV dosimetry to the space conditions. Recently, the effect of short wavelength UV components of the solar radiation on these objects was studied theoretically (Ront o et al., 2002) on bacteriophage T7, while this paper presents the results of the experiment verification tests (EVTs) performed on polycrystalline uracil. Some of the EVT results obtained on bacteriophage T7 and isolated phage DNA are published in this issue (Fekete et al., 2004).
2. Methods The space parameters simulation facilities, available for EVT purposes, are summarized in Table 1.
0273-1177/$30 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2003.07.051
Gy. Ronto et al. / Advances in Space Research 33 (2004) 1302–1305
1303
Table 1 Facilities used in simulation experiments Institution, location
Project name
Principal investigator
Studied parameter
MTA-SE Research Group for Biophysics, HAS, Hungary German Aerospace Medicine, K€ oln, Germany Institute of Space Research, Graz, Austria
PRODEX
G. Ront o
Short wavelength UV
EVT, SSIOUX
G. Horneck, E. Rabbow
Temperature, vacuum
Austrian–Hungarian Scientific Cooperation
H. Lammer, N.I. K€ omle, G. Kargl
Vacuum, short wavelength UV radiation
The polycrystalline uracil thin layers were prepared according to the evaporation technique and the quality of the thin layers was controlled spectroscopically (Gr of et al., 1996; Kerekgy art o et al., 1997). The thickness of the thin layer was optimized for 70 nm. Fig. 1 presents the cross section of the so called sandwich forms of uracil samples: the thin layers are under a vacuumtightly closed fluoride window and an inert gas can be enclosed into the inner volume. Irradiations were performed with low pressure mercury lamp (Tungsram, germicidal lamp; 15 W) and 300 W deuterium lamp (Oriel). The former has a strong characteristic line at k ¼ 254 nm, while the latter is a polychromatic source with a continuous spectrum from 400 down to 200 nm (in atmospheric conditions). The administered UV dose was measured with Polytec AN/ S10 radiometer. Under the influence of UV-B, UV-C irradiation at normal temperature and atmospheric conditions photoproducts (mainly cyclobutane dimers, 6–4 adducts) are formed (Fisher and Johns, 1976; Rosenstein and Mitchell, 1987; Fekete et al., 1998), this effect can be measured by the extent of the decrease of the characteristic absorption (at 280 nm) of uracil (Gr of et al., 1996). For irradiations with germicidal and deuterium lamps dose–effect curves were determined. The effect was expressed as the change of the optical density (OD) value of the irradiated uracil thin layer at the wavelength of 280 nm. The OD value of the uracil samples depends on the thickness of the layer, thus the starting OD values (without irradiation) were standardized by the preparation of the layers. For comparison the starting OD-value was adjusted to 0.45.
3. Results and discussion 3.1. Effect of vacuum The samples were exposed to vacuum in sandwich form with vacuum tightly closed measuring cell at room temperature. Applying either 103 Pa (Graz) or 1.7 104 Pa (K€ oln) for 48 h or 7 days, respectively, no significant change has been detected in the traditional UV spectra of the samples. This result indicates the safe closing of the sandwich samples, however, without covering at room temperature the characteristic absorption spectrum of the uracil disappears indicating the complete evaporation of the substance. 3.2. Effect of temperature The effect of the temperature was tested by incubation of the samples for 7 days at +40 C (DLR, K€ oln). Based on the absorption spectrum of the samples this temperature did not cause any change in the structure of the polycrystalline uracil layer. Taking into account our results obtained earlier with low (down to )20 C) temperature, one can state that the polycrystalline uracil at least in the range from )20 to +40 C is insensitive. Investigation in a broader temperature range as well as the study of the tolerance for the large scale temperature variations that might occur during the flight, will be done in the future in the frame of the EXPOSE-EVT experiment. 3.3. Effect of UV radiation
Fig. 1. Cross section of the uracil samples.
UV exposure of the samples causes a decrease of the OD value (absorbance), indicating the decrease of the intact form of uracil molecules in the thin layer, in other words the extent of the decrease of OD value shows the extent of the photoproduct formation in nucleic acid/in uracil model. Fig. 2(a) shows the decrease of the OD of uracil layers under the influence of the UV irradiation from germicidal lamp, while Fig. 2(b) does the same under the irradiation with deuterium lamp. Both dose–effect curves
1304
Gy. Ronto et al. / Advances in Space Research 33 (2004) 1302–1305
Fig. 2. Decrease of the OD value of uracil thin layer in dependence of UV doses from germicidal (a) and deuterium lamp (b).
having identical starting OD values, show a tendency for saturation, however, the saturation levels differ in the two cases. With germicidal lamp the saturation exists at a lower OD value than with deuterium lamp (at about 60% and 80% of the original OD values, respectively). In Bacillus subtilis spores after exposure to germicidal lamp and to extraterrestrial solar radiation Horneck et al. (1984) demonstrated spore photoproducts (5-thyminyl-5,6-dihydrothymine) and two other products. According to our results the short wavelength UV radiation (UV-B and UV-C), specifically in polycrystalline uracil layers, prefers the formation of cyclobutane dimers (Fidy and Raksanyi, 1978; Gr of et al., 1996; Fekete et al., 1998). In the irradiated uracil sample the lower OD value corresponds to a larger number of photoproducts (in this case photodimers) induced by the irradiation with germicidal lamp, thus the saturation level in Fig. 2(a) corresponds to a higher amount of dimers, than in Fig. 2(b). The presence of the saturation level in the exposed uracil layer in both cases can be interpreted by two simultaneous photoreactions occurring in opposite directions: the photons can either induce the addition of two uracil bases (photoaddition or photodimerization) or can break the dimers into two uracil molecules (monomerization or photoreversion). Both effects were described earlier (e.g. Fisher and Johns, 1976) and were found also in simple biological models (Ront o et al., 1967). The difference between the two saturation levels in Figs. 2(a) and (b) reflect the different levels of the
equilibrium between dimer formation and monomerization. In other words: the shorter wavelength components of deuterium lampÕs spectrum are more efficient in the monomerization reaction of the uracil photoproducts than germicidal lamp, thus the equilibrium occurs at a lower number of dimers. Aiming to study this effect after the previous irradiation with germicidal lamp to saturation, the thin layers were exposed by deuterium lamp. Fig. 3(a). demonstrates the effect: the OD value, characteristic for the germicidal lamp irradiation, increased approximately up to the saturation level obtained with deuterium lamp according to the Fig. 2(b). A second exposure of the samples with germicidal lamp, irradiated former to saturation with deuterium lamp, causes a further decrease of the OD value (Fig. 3(b)). A kinetic model was developed to describe the dose– effect relationship of the monomerization–dimerization reaction induced by the exposure with a constant irradiance dnm ¼ kMD nm þ kDM nd ; dt
ð1Þ
where nm and nd denote the number of monomers and dimers at time t, while kMD and kDM are the rate constants of dimerization and monomerization, respectively. The number of monomers at the time t ¼ 0 can be given as nm ðt ¼ 0Þ ¼ n0m . In a layer containing at the beginning of the irradiation only monomers, the number of monomers can be written at irradiation time t as
Fig. 3. (a) Increase of the OD of UV irradiated uracil thin layer with deuterium lamp. (b) Further decrease of the OD of UV irradiated uracil thin layer with germicidal lamp.
Gy. Ronto et al. / Advances in Space Research 33 (2004) 1302–1305
nm ¼
n0m ½kDM þ kMD eðkMD þkDM Þt : kMD þ kDM
ð2Þ
The initial slope and the saturation level of the dose– effect curves both in Figs. 3(a) and (b) depend on the monomerization and dimerization rate constants and both of them depend on the spectral composition of the UV source. Determination of the wavelength dependence of the rate constants will result in the separate action spectra of monomerization and dimerization is in progress.
4. Conclusions • Uracil dimers in polycrystalline thin layers can be produced by short wavelength irradiation (UV-C) with either germicidal or deuterium lamp, that are detected with spectroscopic methods. • A proportion of the dimers induced with germicidal lamp can be reverted by irradiation with deuterium lamp having shorter wavelength components in emission spectrum. • Using polychromatic source of shorter wavelength (<280 nm) UV radiation, the additive nature (Sutherland, 2002) of the photobiological effect of the different wavelengths is not applicable, thus the modification of the biological UV dosimetry concept and method elaborated for the terrestrial solar radiation should be reconsidered in the use for extraterrestrial dosimetry. • The effect of photoreversion due to short wavelength UV components of the extraterrestrial solar radiation can contribute to the protection of life in the harsh space environment.
Acknowledgements Gy. Ront o, A. Berces, A. Fekete, G. Kov acs and H. € Lammer thank the Osterreichischer Akademischer € Austauschdienst (OAD) for supporting this work as part € of the Austrian–Hungarian OAD-project A-20/2000.
1305
References Fekete, A., Ront o, Gy., Heged€ us, M., M odos, K., Berces, A., Kovacs, G., Lammer, H., Panitz, C., Simulation experiments of the space environment on bacteriophage and DNA thin films. Adv. Space Res., 2004, in press. Fekete, A., Vink, A.A., Gaspar, S., Berces, A., M odos, K., Ront o, G., Roza, L. Assessement of the effects of various UV sources on inactivation and photoproduct induction in phage T7 dosimeter. Photochem. Photobiol. 68, 527–531, 1998. Fidy, J., Raksanyi, K. Spectroscopic and kinetic study of UV photochemistry of uracil thin layers. Studia Biophys. 71, 137– 138, 1978. Fisher, G.J., Johns, H.E. Pyrimidine photodimers, in: Wang, S. (Ed.), Photochemistry and Photobiology of Nucleic Acids, vol. 1. Academic Press, New York, pp. 225–294, 1976. Gr of, P., Gaspar, S., Ront o, Gy. Use of uracil thin layer for measuring biologiocally effective UV dose. Photochem. Photobiol. 64, 800– 806, 1996. Horneck, G., B€ ucker, H., Reitz, G., Requardt, H., Doose, K., Martens, K.D. Microorganisms in the space environment. Science 225, 226–228, 1984. Horneck, G., Wynn-Williams, D.D., Mancinelli, R.L., Cadet, J., Munakata, N., Ront o, G., Edwards, H.G.M., Hock, B., W€anke, H., Reitz, G., Dachev, T., H€ader, D.P., Brioullet, C., Biological experiments on the EXPOSE facility of the International Space Station, in: Proceedings of the Second European Symposium on the Utilization of the ISS, vol. ESA SP-433, pp. 459–468, 1999. Kerekgyart o, T., Gr of, P., Ront o, G. Production and basic application of uracil Dosimeters for measuring the biologically effective UV dose. Centr. Eur. J. Occup. Environ. Med. 3, 143–152, 1997. Rettberg, P., Rotschild, L. Ultraviolet radiation in planetary atmospheres and biological implications, in: Horneck, G., BaumstarkKahn, C. (Eds.), Astrobiology. Springer, Berlin, pp. 233–243, 2002. Ront o, G., Sarkadi, K., Tarjan, I. Zur analyse der UV dosiswirkungskurven der T7 bakteriophagen. Strahlentherapie 134, 151–157, 1967. Ront o, G., Gapar, S., Berces, A. Phage T7 in biological UV dose measurement. J. Photochem. Photobiol. B 12, 285–294, 1992. Ront o, G., Gaspar, S., Fekete, A., Kerekgyart o, T., Berces, A., Gr of, P. Stability of nucleic acid under the effect of UV radiation. Adv. Space Res. 30, 1533–1538, 2002. Rosenstein, B.S., Mitchell, D.L. Action spectra for the induction of pyrimidine (6–4) pyrimidone photoproducts and cyclobutane pyrimidine dimers in normal human skin fibroblasts. Photochem. Photobiol. 45, 775–780, 1987. Sutherland, J.C. Biological effects of polychromatic light. Photochem. Photobiol. 76, 164–170, 2002. Weber, P., Greenberg, J.M. Can spores survive in interstellar space? Nature 316, 403–407, 1985.