Life sciences: microorganisms in the space environment.

Preliminary results of the Spacelab 1 experiment on the response of Bacillus subtilis spores to conditions of free space are presented. Exposure to the vacuum of space on the Spacelab pallet reduced viability counts about 50 percent and increased mutation frequencies by a factor of about 10. Interpretation of apparent differences in the photobiological and photochemical data between flight and ground simulation experiments will require more statistical analyses and data from actual fluence measurements.

Microorganisms and biomolecules in space environment experiment ES 029 on Spacelab-1.

Bacterial spores are proper test organisms for studying problems of space biology and exobiology. During the Spacelab 1 mission, studies on the limiting factors for survival of Bacillus subtilis spores in free space have been performed. An exposure tray on the pallet of Spacelab 1 accomodated 316 samples of dry spores for treatment with space vacuum and/or the following selected wavelengths of solar UV: > 170 nm, 220 nm, 240nm, 260nm and 280 nm. After recovery, inactivation, mutation induction, reparability, and photochemical damages in DNA and protein have been studied. The results contribute to the understanding of the mechanisms of increased UV sensitivity of bacterial spores in vacuo and to a better assessment of the chance of survival of resistant forms in space and of interplanetary transfer of life.

Photobiology in space: an experiment on Spacelab I.

The joint European/US Spacelab Mission I, scheduled for October 1983 for a 9 day lasting Earth-orbiting flight, provides a laboratory system for various disciplines of science, including exobiology. On the pallet, in the experiment ES 029 "Microorganisms and Biomolecules in Space Hard Environment" 316 dry samples of Bacillus subtilis spores will be exposed to space vacuum and/or selected wavelenghs of solar UV radiation. After recovery action spectra of inactivation, mutation induction, reparability and photochemical damage in DNA and protein will be determined. The results will contribute to the understanding of the mechanism of the increased UV sensitivity of bacterial spores in vacuo and to a better assessment of the chance of survival of resistant life forms in space and of interplanetary transfer of life.

Dependence of the mutagenic power of heteroatomic dyes on their DNA-base-pair specificity.

23 compounds structurally related to proflavine were tested with Salmonella typhimurium TA1537 for their ability to induce mutants in the quantitative mutagenicity test of Ames et al. Of these compounds, 13 were mutagenic. Their mutagenic power decreased with increasing GC specificity of the dye. Because the mutational site in the tester strain is assumed to consist of a run of 4 adjacent GC pairs of the same polarity we conclude that for mutation to occur the dye should not be bound within this run of identical base pairs. Some of the compounds showed a negative slope at higher concentrations. Because these dyes also showed a comparatively high tendency to dimerize we conclude that mutation induction requires the intercalator to be bound as a monomer. Those compounds that were not mutagenic either did not intercalate or were inactivated by reduction.

Survival and mutagenesis in UV-irradiated phage: multi-hit kinetics of mutation induction and lack of indirect induction by infection with UV-irradiated phage of error-prone repair.

The paper is concerned with the question of whether WEIGLE-reactivation (WR) and WEIGLE-mutagenesis (WM) can be indirectly induced by infection with UV-irradiated phage. Experiments neither with phage lambda of Escherichia coli nor with phage chi of Serratia marcescens show such induction-In this respects phage DNA differs from F'-DNA or Hfr-DNA; possible explanations are discussed. In both systems clear phage mutations can also be induced by UV without irradiation of the host cells; they appear, in unirradiated and irradiated host cells, with an increase of frequency which is greater than proportional to the UV dose. It is concluded that mutation induction of phage in the unirradiated host cells is due to a low level constitutive mutagenic repair; this could either be due to "spontaneous" induction of the mutagenic SOS-function or it could be a mechanism different from this one. Host irradiation would give rise to additional activity by the induced SOS-function leading to WR and WM. It is further concluded that deviation of the induction kinetics from a linear dose-dependence is not due to the necessary induction of SOS-functions.

Mutation induction by thymine deprivation in Escherichia coli B/R. II. Mutation in the repressed and derepressed tryptophan operon.

True Trp+ reversions are induced by thymine deprivation in cells with repressed trp operons as efficiently as in derepressed cells. At least part of the mutations are fixed during thymine starvation, i.e. in the absence of net DNA synthesis. The hypothesis is put forward that thymineless mutagenesis is due to repair-replication under limited concentrations of 5'-dTTP, performed by an inducible error-prone "DNA-polymerizing activity" on single-strand gaps.

Mutation induction by thymidine deprivation in Escherichia coli B/r. I. Influence of caffeine.

The addition of caffeine to the plating medium after thymine deprivation of E. coli WP2 uvr+ thyA or WP2 uvrA thyA had no influence on survival. Caffeine, however, reduced the frequency of mutants. The hypothesis is presented that the reduced mutagenesis is due to the sensitivity to caffeine of an inducible error-prone repair mechanism operating during thymine deprivation and after the re-addition of thymine.

Kinetics of thymineless death in Escherichia coli 15 as measured by single-cell observations.

Kinetics of thymineless death for Escherichia coli 15 TAU-bar from plating on solid medium were compared with those from direct observations of single cells under a microscope. The latter method did not involve any physical change of the medium. The kinetics obtained for the two methods were identical. This rules out the assumption that in E. coli 15 TAU-bar death from the thymine deprivation is directly associated with the plating procedure.

[Inactivating and mutagenic effects of long-wave UV-light in bacteria with various mechanism of repair]. / Die inaktivierende und mutationsauslösende Wirkung von langwelligem UV-Licht bei Bakterien mit verschiedenen Reparatur-Mechanismen

UV-radiation of 254 nm wavelength produces in the genetic material (desoxyribonucleic acid, (DNA) of bacteria photochemical alterations (lesions) which can lead to cellular death or mutation induction. The biologically most important class of these lesions is the one of the pyrimidine dimers. Bacteria possess three groups of enzymatic mechanisms which can eliminate such lesions under certain circumstances: elimination in situ; removal from the nucleotide chain (prereplication repair); ignoring the lesion (postreplication repair). The biological effect and the importance of these so-called repair mechanisms is reviewed and the occurrence in other organisms is briefly discussed. On the one hand, organisms are exposed to UV-radiation of 254 nm wavelength only under artificial conditions; on the other hand, long-wave solar UV-radiation (between approximately 300 nm and visible light) which amounts to about three per cent of the total energy output, represents the most powerful radiation to which organisms can be exposed under natural conditions to any larger extent. As outlined in the second part of this review, this radiation also induces lesions which may act as substrate for the above mentioned repair mechanisms. With increasing wavelength, lesions may also occur in cellular components other than DNA. The complexity of biological responses arising thereby is discussed.

Photoreactivation of bacteriophage phi chi 174.

U.V.-irradiated single-stranded DNA-bacteriophage phi chi 174 shows a photoreactivable sector of 0-17. That this sector is relatively small compared with those for the double-stranded DNA-phages T2 and T6 (about 0-5) does not necessarily seem to be due to the pyrimidine dimers in single-stranded DNA being intrinsically a poorer substrate for the photoreactivating enzyme. This follows from the observation that intracellularly irradiated single-stranded phi chi 174 DNA also shows a photoreactivable sector of 0-4 to 0-5. The same value is obtained for intracellularly irradiated double-stranded phi chi 174 DNA. Photoreactivation of intracellularly irradiated single-stranded phi chi 174 DNA is not constant with U.V. dose for the lower dose ranged. Possible explanations for this are discussed.