Biomedical subjects

H Bucker

Publications and source records attributed to H Bucker.

At least 37 records · Page 2Linked to original sources

PubMed1984

Unique radiobiological aspects of high-LET radiation.

Since the beg inning of manned space flight the potentially unique radiobiological properties of the heavy ions of the cosmic radiation had been, apart from possible interactions of radiation effects with biological effects of weightlessness, of major concern with respect to the assessment of radiation hazards in manned space flight. Radiobiological findings obtained from space flight experiments and ground based experiments with densely ionizing radiation are discussed, which suggest qualitative differences between the radiobiological mechanisms of sparsely ionizing and densely ionizing radiation. These findings comprise the observation of a long lateral range of radiobiological effectiveness around tracks of single heavy ions, the observation of micro lesions induced in biological targets by the penetration of heavy ions, the nonadditivity of radiobiological effects from sparsely and densely ionizing radiation, the different kinetics for the expression of late effects induced by sparsely or densely ionizing radiation, and the observation of a reversed dose rate effect for early and late effects induced by densely ionizing radiation. These findings bear on the radiation protection standards to be installed for a general public in manned space flight and on the design of experiments, which intend to contribute to their specification.

Cosmic Radiation↗

PubMed1983

Inactivation, mutation induction and repair in Bacillus subtilis spores irradiated with heavy ions.

Studies on the response of bacterial spores to accelerated heavy ions (HZE particles) help in understanding problems of space radiobiology and exobiology. Layers of spores of Bacillus subtilis strains, differing in repair capabilities, were irradiated with accelerated boron, carbon and neon ions of linear energy transfer (LET) values up to 14000 MeV cm2/g. Inactivation as measured by loss of colony forming ability and induction of mutations as measured by reversion to histidine prototrophy and resistance to 150 micrograms/ml sodium azide were tested, as well as the influence of repair processes on these effects. For inactivation, the cross-sectional values sigma plotted as a function of LET follow a saturation curve. The plateau, which is reached around a LET of 2000 MeV cm2/g, occurs at 2.5 x 10(-9) cm2, a value in good agreement with the dimensions of the spore protoplast. Lethal damage produced at LET values < 2000 MeV cm2/g is reparable. Recombination repair is more effective than excision repair. At higher LET values, lethal damage could not be reconstituted by the repair mechanisms studied. In addition, at these high LET values, the frequency of induced mutations was drastically decreased. The data support the assumption of at least two qualitatively different types of lesion, depending on the LET of the affecting heavy ion.

Bacillus subtilis↗

PubMed1983

Inactivation probability of heavy ion-irradiated Bacillus subtilis spores as a function of the radial distance to the particle's [correction of paricle's] trajectory.

The understanding of the radiobiological action of heavy ions requires the knowledge of the dependence of the inactivation probability on the distance between the particle's trajectory and the biological test organism (the impact parameter). Spores of Bacillus subtilis with a cytoplasmic core of about 0.22 micrometer cross section are suitable test objects for the study of this radial inactivation probability in its microscopic details. The spores are irradiated at low fluences of some 10(6) ions/cm2 with very heavy ions at different specific energies up to 10 MeV per atomic mass unit u while in fixed contact with visual nuclear track detectors. The methods are described by which the biological response of individual cells can be evaluated and the impact parameter be determined with an accuracy typically better than 0.2 micrometer. The results demonstrate that the common characteristics of inactivation, e.g., an effective range of inactivation extending to at least 3 micrometers, a nonmonotonic dependence of the inactivation probabilities on the radial distance, and the fact that the inactivation probability even for direct central hits on the cytoplasmic core is substantially below one, are nearly independent of the particle energy and type. The results are incompatible with the assumption that the radiobiological effectiveness can be attributed to the dose of secondary electrons as currently understood. They also demonstrate that the widely held notion of an "overkill" at low impact parameters does not apply for the spores even with the most densely ionizing ions.

Argon↗

PubMed1980

Recent radiobiological findings from spaceflight and ground-based studies--an overview.

With respect to radiation standards for manned space flight, we wish to address ourselves to the following topics that we consider pertinent for a realistic assessment of the risk to man when exposed to ionizing radiation under space flight conditions: 1) prediction and measurement of the spectra of the physical traits of cosmic radiation as a function of orbital parameters and the mass shielding of the spacecraft; 2) synergistic or antagonistic modification of radiation effects by dynamic flight conditions and by the space environment; 3) production of biological damage becoming manifest only long after exposure, especially to the heavy ions; and 4) demonstration of possibly specific radiobiological mechanisms for the densely ionizing heavy-ion component of the cosmic radiation. Some recent work referring to these topics will be presented and discussed with emphasis on the high LET component of the cosmic radiation.

Animals↗

PubMed1979

A special photoproduct of UV-irradiated DNA in vacuo.

DNA isolated from E. coli B/r cells was UV-irradiated at 254 nm under high vacuum of 10(-7) torr. Compared with DNA in solution, the formation of cis-syn thymine dimers (TT) was decreased, and the formation of cytosine thymine dimers (CT) and a photoproduct of RF value 0.41 was increased. The latter photoproduct was identified as tran-syn TT which is preferentially produced in heat-denaturated DNA.

DNA Damage↗

PubMed1979

Dosimetric and biological results from the Bacillus subtilis Biostack experiment with the Apollo-Soyuz Test Project.

The evaluation of the Bacillus subtilis experiment has been completed. The biological and the physical results for this part of the Apollo-Soyuz Test Project (ASTP) Biostack experiment are given. This comprises dosimetric data for the cosmic radiation at that orbit as well as biological findings from two types of plastic detectors. Further, the frequency distributions of the physical quantities atomic number, energy and energy loss of the heavy ions within the sample of spores hit are presented. The biological hazard presented by cosmic HZE-particles has been much underestimated.

Bacillus subtilis↗

PubMed1978

Radiobiological results from the Bacillus subtilis Biostack experiments within the Apollo and the ASTP space flights.

In order to check the results of earlier Biostack experiments, new experimental techniques were developed for the Biostack III experiment in the Apollo-Soyuz test project (ASTP). These techniques resulted in an increased accuracy of localization down to 0.2 micrometers for the determination of the impact parameter, accompanied by an increase in the sample size available for biological investigation. In addition, colony forming ability, metabolic mutations, and mutations affecting UV- and x-ray sensitivity were rendered observable by these methods. The biological and physical results obtained so far from the evaluation of the Bacillus subtilis experiment within Biostack III confirm and extend the findings of the previous Biostack experiments. They also add to the questions about the mechanisms of action of the radiation field under investigation, since the observed effects cannot be interpreted in terms of standard concepts.

Bacillus subtilis↗

PubMed1976

Effect of space factors on Escherichia coli B/r cells.

Stationary phase cells of Escherichia coli B/r were inactivated when they were exposed to high vacuum (10(-6) torr). About 5% of the cells were still able to form a colony after 45 min exposure. Vacuum dried cells (0.5 torr, 120 min) show colony forming ability of 30% or more. They were inactivated to about 5% by further vacuum treatment. Vacuum treated cells showed higher permeability for various cell components. UV irradiated E. coli B/r cells in vacuum showed increased UV sensitivity. DNA-protein cross-links were preferentially formed in a vacuum. To obtain 63% of DNA cross linked with protein required 852 erg mm-2 (D37) of UV irradiation in suspension and only 72 erg mm-2 of UV irradiation in vacuum. The protein components of DNA-protein cross-links were hydrolysed with pronase E and the amino acids directly bonding to DNA were determined. The most important amino acids concerned in DNA-protein cross-links seem to be glycine and alanine, followed by aspartic acid (asparagine), glutamic acid (glutamine) and histidine. The sensitivity to X-rays of stationary phase E. coli B/r cells seems to depend on the remaining gas atmospheric in the vacuum since it varies with different pumping systems.

Amino Acids↗

PubMed1976

The Biostack as an approach to high LET research.

By simple geometric and dosimetric arguments the advantage of an experimental approach to high LET radiation research is demonstrated. The Biostack is capable of recording individual hits of heavy ions on single biological targets. This improved method is compared with the common experimental methods for studying biological effects with high LET radiation and is suggested as an methodological improvement in fundamental research.

Cosmic Radiation↗

PubMed1976

Localization and track evaluation of HZE particles.

A new method of track-etching was developed called "individual etching", allowing increased accuracy of the localization whereby a latent track is developed under microscopic control. The influence of the humidity of the detectors at the beginning of the etch process was investigated. This influence consists in an increase of bulk and track etching rate. The scattering in experimental data, which is mostly attributed to the inhomogeneity of the material, can be partially explained by this effect, especially the difference in isotopic resolution between accelerator experiments and cosmic-ray flights.

Bacillus subtilis↗

PubMed1975

Radiobiological results of the Biostack experiment on board Apollo 16 and 17.

After penetrating the Biostack capsule, some of the HZE particles hit the biological objects carried: bacterial spores (Bacillus subtilis), seeds (Arabidopsis thaliana and Vicia faba), and shrimp eggs (Artemia salina). The different biological objects were affected by heavy ions in widely varying ways. A broad range of radiobiological investigations has been carried out in regard to the objects' response to HZE particles. The most sensitive biological objects in the Biostack experiments proved to be the shrimp eggs. The development of 500 eggs hit by heavy cosmic ions was investigated. This differed significantly from the flight controls (eggs flown in the Biostack but not hit by heavy ions) and from the ground controls. From this it has been concluded that penetration on the part of a single heavy ion may injure the encysted blastula. This damage was found to influence gastrula formation and even the hatching process of the nauplius. Abnormalities (increased by a factor of 10) in the orthonauplius were observed during the development of the hit eggs; they consisted, for example, of shortened extremities or an abnormal thorax or abdomen. In addition, eggs of Tribolium confusum and Carausius morosus, which were included in Biostack 2 (Apollo 17), have been investigated, and the influence of single heavy ions on the development process of these highly organized insects has been studied.

Abnormalities, Radiation-Induced↗

PubMed1975

Results of the Bacillus subtilis unit of the Biostack II experiment: physical characteristics and biological effects of individual cosmic HZE particles.

The effectiveness of cosmic HZE-particles on unicellular procaryotic, organisms was studied on Bacillus subtilis spores, which were accommodated in the Biostack I and II experiments on board Apollo 16 and 17. Identification of the spores that were hit was achieved by using the Biostack sandwich construction and by precise microscopical measurements of tracks of particles. Germination, outgrowth and the rate of cellular elongation were investigated. A method was developed to determine the charge of each individual HZE particle that penetrated a spore and its energy loss in the region of hit. An attempt was made to establish a connection between these physical characteristics and the biological effects produced.

Bacillus subtilis↗

PubMed1975

Membrane damage in dehydrated bacteria and its repair.

The dehydration of bacteria by vacuum exposure results in damage to the cell membrane. This membrane damage does not necessarily lead to cell death. A part of the dehydrated bacteria is capable of eliminating the membrane damage by repair processes. Repair can proceed rapidly under conditions that permit synthesizing activities. The kinetics of this repair process were studied by means of the membrane-mediated biosynthesis of the cell wall as well as by the recovery of resistance to small concentrations of lysozyme. Repair is a precondition for cell proliferation. At low temperature cells can conserve their membrane damage and the repair process can be initiated when conditions become favourable.

Cell Division↗

PubMed1974

Viability of Bacillus subtilis spores exposed to space environment in the M-191 experiment system aboard Apollo 16.

During the Apollo 16 space flight, in the experiment system M-191, (microbial response to space environment) spores of Bacillus subtilis 168 were exposed to space vacuum or solar UV irradiation with a peak wavelength of 254 nm or both. The effects of these space factors on the colony-forming ability of the spores were studied. It was found (i) that space vacuum alone did not affect the survival of pre-dried spores; (ii) that space vacuum in combination with solar UV irradiation with a peak wavelength of 254 nm had a synergistic effect, which may by attributed to a UV supersensitivity of the spores during vacuum exposure. These results agreed with findings of simulation experiments on earth. It was concluded that air dried spores may survive exposure to space vacuum if shielded against solar UV irradiation.

Bacillus subtilis↗

PubMed1974

The Biostack Experiments I and II aboard Apollo 16 and 17.

The concept of the Biostack experiment has become practicable through European scientific collaboration and with help of NASA. The objectives of this experiment flown aboard Apollo 16 and 17 are to study the biological effects of individual heavy cosmic particles of high-energy loss (HZE) not available on earth; to study the influence of additional spaceflight factors; to get some knowledge on the mechanism by which HZE particles damage biological materials; to get information on the spectrum of charge and energy of the cosmic ions in the spacecraft; to estimate the radiation hazards for man in space. For this purpose the Biostack experiment comprises a widespread spectrum of biological objects, and various radiobiological end-points are under investigation. Bacterial spores, protozoa cysts, plant seeds, shrimp eggs, and insect eggs were included in the Biostack experiment packages together with different physical radiation detectors (nuclear emulsions, plastics, AgCl crystals, and LiF thermoluminescence dosimeters). By using special arrangements of biological objects and physical track detectors, individual evaluation of tracks was obtained allowing the identification of each penetrating particle in relation to the possible biological effects on its path. The response of the different biological objects to space flight and HZE ions bombardment was of different degree, presumably depending on the ability of the organism to replace the cells damaged by a hit. The results help to estimate the radiation hazard for astronauts during space missions of long duration.

Animals↗

PubMed1973

The Biostack experiment on Apollo 16.

The object of the Biostack experiment is to study the biological effects of high ZE particles of cosmic radiation in order to obtain information on the mechanism of these particles in biological matter. For this purpose individual local evaluation methods have been developed which allow one to identify each biologically effective particle and to correlate the individual hitting particle with the biological effect produced. The Biostack experimental package contains a series of monolayers of selected biological objects (Bacillus subtilis spores, Arabidopsis thaliana seeds, Vicia faba radiculae, Artemia salina eggs) with each layer sandwiched between several different cosmic ion track detectors (nuclear emulsions, cellulose nitrate, polycarbonate). By this arrangement a variety of biological effects due to a single penetrating particle can be analysed. Influence on cellular and tissue development, nuclear damages, and mutation induction are the main investigated effects. These space flight findings will be completed by results of balloon flight and accelerator experiments.

Animals↗

PubMed1973

Solid state AgCl detectors for nuclear tracks with on- and off-response at choice: applications to life sciences.

A new concept of trackforming solid state detectors is presented. These detectors record and accumulate tracks of ionizing particles which can be revealed if they are irradiated with yellow light during the passage of the particle through the detector; otherwise the tracks are dropped by fading. Tracks stabilized by yellow light are stable for months. The detectors consist of thin layers of 200-300 micrometers of Cd-doped AgCl crystals, supported by a thin plate of quartz glass. The invisible latent tracks in these detectors are revealed at microscopically visible size by ultraviolet light. The sensitivity of the crystals against particles of different specific energy transfer depends upon the concentration of Cd; these have rather good thresholds, which permit selective recording in a well-known manner. These AgCl(Cd) crystals have a unique property amongst trackforming detectors; their response can be switched on and off at choice, for instance by electronic triggering of the stabilizing accompanying yellow light. This allows a time assignment of particle tracks, or restriction to tracks of desired particles. Examples of tracks and of applications in cosmic ray research, heavy ion physics, radiobiology and dosimetry are given.

Bacillus subtilis↗

PubMed1972

Effects of simulated space vacuum on bacterial cells.

The effect of vacuum on bacterial cells is related to water desorption. Below water vapour pressure the inactivation remains constant, independent of total pressure and exposure time. In subsequent growth, the lag-phase of the survivors is delayed. Combined treatment with vacuum and radiation (X-rays or uv of 254 nm wavelength) results in synergistic effects, whereas vacuum and heat can act antagonistically. The vacuum inactivated cells (indicated as loss of colony-forming ability) are completely damaged. They do not show cellular elongation, phage production or respiration. The cellular membrane becomes permeable by vacuum exposure: biomolecules are released from the cells when re-suspended after vacuum treatment.

Bacillus subtilis↗