Gy. Rontó

Phages T7 in biological UV dose measurements

An experimental method complete with theoretical considerations is presented for the measurement of different biological UV doses. The method is based on the high sensitivity of phage T7 activity to UV light. A precisely determined T7 inactivation action spectrum is presented over a wide optical range (240-514 nm). Using the T7 spectral sensitivity in relation to the minimal erythema dose (MED) and the effective spectral irradiance from solar radiation for the MED, an example is given to determine the MED value based on the measurement of T7 inactivation for a given case. The advantages and applicability of the method are discussed.

ULTRAVIOLET DOSIMETRY IN OUTDOOR MEASUREMENTS BASED ON BACTERIOPHAGE T7 AS A BIOSENSOR

A simple method has been worked out for measuring the biologically effective dose (BED) of solar radiation The method uses phage T7 as a biosensor and it includes field measurements of global and direct UV radiation from the sun in the air; it has been applied to underwater measurements as well. Results of field measurements are presented with discussion of the angle‐dependent sensitivity of the biosensor. A model of spectral irradiance based on the measured values is presented. Relevance of the HT7 unit—derived earlier by us from T7 phage inactivation upon UV radiation—as a measure of the BED is also discussed.

Assessment of the Effects of Various UV Sources on Inactivation and Photoproduct Induction in Phage T7 Dosimeter

The correlation between the biologically effective dose (BED) of a phage T7 biological dosimeter and the induction of cyclobutane pyrimidine dimers (CPD) and (6‐4) photoproducts ((6‐4)PD) in the phage DNA was determined using seven various UV sources. The BED is the inactivation rate of phage T7 expressed in HT7 units. The CPD and (6‐4)PD were determined by lesion‐specific monoclonal antibodies in an immunodot‐blot assay. The various lamps induced these lesions at different rates; the relative induction ratios of CPD to (6‐4)PD increased with increasing effective wavelength of irradiation source. The amount of total adducts per phage was compared to the BED of phage T7 dosimeter, representing the average number of UV lesions in phage. For UVC (200–280nm radiation) and unfiltered TL01 the number of total adducts approximates the reading; however, UV sources having longer effective wavelengths produced fewer CPD and (6‐4)PD. A possible explanation is that although the most relevant lesions by UVC are the CPD and (6‐4)PD, at longer wavelengths other photoproducts can contribute to the lethal damage of phages. The results emphasize the need to study the biological effects of solar radiation because the lesions responsible for the lethal effect may be different from those produced by various UV sources.

Biological UV dosimetry-a comprehensive problem

Abstract The biologically effective dose from environmental radiation was measured using phage T7 and uracil thin layer sensors in a dosimeter developed previously (Gy. Ronto, S. Gaspar and A. Berces, Phages T7 in biological UV dose measurement, J. Photochem. Photobiol. B: Biol., 12 (1992) 285–294; P. Grof, S. Gaspar and A. Berces, Uracil thin layers in dosimetry of UV radiation, Proc. Int. Symp. Budapest Biomedical Optics, Europe, 1993 , to be published). Examples of measured daily and annual profiles are presented to demonstrate the possibilities and limits of biological dosimetry. In addition, phage T7, uracil sensor and Robertson-Berger meter results are compared. A comparison of model calculation data with the measured values is presented. On the basis of the results obtained, the application of biological dosimeters in both long-term field measurements and laboratory experiments is suggested.

Influence of phage proteins on formation of specific UV DNA photoproducts in phage T7

Abstract— Phage T7 can be used as a biological UV dosimeter. Its reading is proportional to the inactivation rate expressed in HT7 units. To understand the influence of phage proteins on the formation of DNA UV photoproducts, cyclobutane pyrimidine dimers (CPD) and (6–4)photoproducts ((6–4)PD) were determined in T7 DNA exposed to UV radiation under different conditions: intraphage T7 DNA, isolated T7 DNA and heated phage. To investigate the effects of various wavelengths, seven different UV sources have been used. The CPD and (6–4)PD were determined by lesion‐specific antibodies in an immunodotblot assay. Both photoproducts were HT7 dose‐dependently produced in all three objects by every irradiation source in the biologically relevant UV dose range (1–10 HT7). The CPD to (6–4)PD ratios increased with the increasing effective wavelength of the irradiation source and were similar in intraphage T7 DNA, isolated DNA and heated phage with all irradiation sources. However, a significant decrease in the yield of both photoproducts was detected in isolated T7 DNA and in heated phage compared to intraphage DNA, the decrease was dependent on the irradiation source. Both photoproducts were affected the same way in isolated T7 DNA and heated phage, respectively. The yield of CPD and (6–4)PD was similar in B, C‐like and A conformational states of isolated T7 DNA, indicating that the conformational switch in the DNA is not the decisive factor in photoproduct formation. The most likely explanation for modulation of photoproduct frequency in intraphage T7 DNA is that the presence of bound phage proteins induces an alteration in DNA structure that can result in an increased rate of dimerization and (6–4)PD production of adjacent bases in intraphage T7 DNA.

Monitoring of environmental UV radiation by biological dosimeters

As a consequence of the stratospheric ozone layer depletion biological systems can be damaged due to increased UV-B radiation. The aim of biological dosimetry is to establish a quantitative basis for the risk assessment of the biosphere. DNA is the most important target molecule of biological systems having special sensitivity against short wavelength components of the environmental radiation. Biological dosimeters are usually simple organisms, or components of them, modeling the cellular DNA. Phage T7 and polycrystalline uracil biological dosimeters have been developed and used in our laboratory for monitoring the environmental radiation in different radiation conditions (from the polar to equatorial regions). Comparisons with Robertson-Berger (RB) meter data, as well as with model calculation data weighted by the corresponding spectral sensitivities of the dosimeters are presented. Suggestion is given how to determine the trend of the increase in the biological risk due to ozone depletion.

COMPLEX METHOD FOR THE DETERMINATION OF THE PHYSIOLOGICAL PARAMETERS OF BACTERIUM–PHAGE SYSTEMS

Publisher Summary This chapter discusses the comparison of three experimental methods and the connected theoretical ones developed for the determination of the physiological parameters of bacterium–phage complexes. The first method was applied to a continuous culture, the second one to a batch culture, and the third one was an automatized evaluating system. The methodics presented for E. coli B–T7 phage systems are applicable for the analysis and quantitative description of any physical, chemical effects on bacteria, phages, and phage–bacterium systems. This chapter discusses what information can be obtained from the determined parameters and from their changes. The parameters remain stable only if the physiological conditions of the culture remain constant for a long time. This stability can be ensured with a chemostat. From the properties of the chemostat follows the formation of a self-regulating system of bacteria that keeps a fixed doubling rate in spite of various substrates and influencing agents. This means that in the chemostat within certain limits, the influence of external effects can be totally compensated.

Construction of spectral sensitivity function using polychromatic UV sources

A procedure is presented for constructing the spectral sensitivity functions of biological dosimeters, using five polychromatic UV sources possessing different emission spectra. Phage T7 and uracil biological dosimeters have been used for measuring the dose rates of the lamps. Their spectral sensitivity functions consisting of two exponential terms have been constructed. The parameters of the spectral sensitivity functions have been determined by comparing the directly measured and calculated dose-rate values. The parameters of the sensitivity function are accepted as correct values when the deviation of the measured and calculated values is a minimum. Based on the deviations between the constructed and the experimentally determined spectral sensitivities with monochromatic sources, the differences between the measured and calculated results are interpreted. The importance of the correct spectral sensitivity data is demonstrated through the effectiveness spectra of a TL 01 lamp for phage T7 killing, uracil dimerization and erythema induction.

Biological UV Dosimeters in Quality Control of Tanning Tubes

Abstract Although according to the International Radiological Protection Association–International Non-Ionizing Radiation Committee recommendation (1991) the use of sunbeds for cosmetic purposes is not recommended, tanning devices are used widely. Ten different types of commercially available sunbed tubes have been studied using a uracil biological UV dosimeter, and three of them were analyzed in detail. Dimerization effectiveness of the tubes was measured directly, whereas efficiency of erythema induction was calculated weighting the emission spectra by the Commission Internationale de lEclairage erythema action spectrum. The data obtained demonstrate that quality control of sunbed tubes has to include not only the determination of the UV doses administered but also the assessment of the health risk due to the UVB and UVA components of the lamp. A method of quality control using the uracil biological dosimeter was elaborated, and the estimation of the “acceptable” exposure time was checked/controlled on 15 volunteers by assessing individually the erythema induction threshold. A correct classification of the sunbed tubes is proposed by characterizing the erythema induction versus DNA-damaging effectiveness of tubes.