Akira Matsuyama

Mechanism for Radiation Lethality in M. Radiodurans

SummaryAfter irradiation with doses which yield almost 100 per cent survival using ordinary agar plating methods, the cells of M. radiodurans lost their colony-forming ability when the post-irradiation incubation was carried out in the presence of inhibitors of protein or RNA synthesis. This result suggests the relative importance of protein and/or RNA synthesis as primary targets for the killing action of radiation.

ALKALI HALIDES AS AGENTS ENHANCING THE LETHAL EFFECT OF IONIZING RADIATIONS ON MICROORGANISMS.

MATSUYAMA, AKiRA, NAMIKI, MITSUO, AND OKAZAWA, YOSHISHIGE. Alkali Halides as Agents Enhancing the Lethal Effect of Ionizing Radiations on Microorganisms. Radiation Res. 30, pp. 687-701 (1967). Actions of alkali halides such as fluoride, chloride, bromide, and iodide were found to enhance the lethal effect of ionizing radiations on cells of bacteria and yeast suspended in 0.067 M phosphate buffer. The data obtained are concerned mainly with the effects of halides present during irradiation. The effects of halide concentration, dose, pH, and freezing on the enhancing actions of halides and also on the aftereffects of irradiation were determined. It was concluded that the possible mechanism for the enhancement by halides may involve the inactivation of a multihit type of short-lived species, which is produced from halide ions by ionizing radiations, but not by ultraviolet light. Different halides, however, appeared to behave differently toward irradiation with respect to forming the longlived species which could have an influence on the enhancement of radiolethality.

LET-Dependent Radiosensitivity of Escherichia coli K-12 rec and uvr Mutants

Escherichia coli K-12 AB1157 (rec/sup +/uvr/sup +/), AB2500 (uvrA), AB2470 (recB), and JC1553 (recA), which have different DNA repair capacity, were bombarded with ..cap alpha.. particles, C ions, and N ions having various beam energies in order to determine the LET-dependent radiosensitivity. Radiosensitivity of the uvrA mutant was almost the same as that of the wild-type throughout the whole LET region studied. Difference in radiosensitivity between the rec- mutants and the wild-type was found to decrease with increasing LET of charged particles used. Such LET dependence can be explained by the increase in the ratio of irreparable to reparable-type damages in DNA with the increasing LET of the particles. It is also possible that a significant component of the LET-dependent changes in viability observed may be due to damages to the repair system itself.

Loss of characteristic radiation resistance by mutation of Micrococcus radiodurans

Abstract The exceptional radioresistance of M. radiodurans was lost by a mutation, and the isolated mutant, KH840, had almost the same radiosensitivity as E. coli K12 AB1157 or B/r. DNA-strand scissions in this mutant were rejoined partly during post-irradiation incubation. Reduced DNA polymerizing activity and extensive degradation of the product was observed in vitro in the crude extract from the sensitive strain. The lower repair capability is not accompanied by the reduced transformation frequency.

Isolation and some radiobiological properties of mutants of Micrococcus radiodurans sensitive to ionizing radiations.

Five partially temperature-sensitive mutants were isolated from wild-type Micrococcus radiodurans. Radiosensitivity of the mutants has been determined. The restitution process in the mutants was relatively sensitive to radiation. The delayed DNA repair in the mutants was due to an alteration of the restitution process, but not to change in degradation system. The enhanced cell death in the mutant cell is closely associated with delayed DNA repair.

Mutagenicity tests of irradiated onions by Escherichia coli mutants in vitro

Abstract Sprout inhibition of onion bulbs can be effectively accomplished by low doses of radiation [2,3]. However, wholesomeness data on irradiated onions, particularly with respect to their mutagenic activity, are still insufficient for evaluation [6]. Therefore we examined the mutagenic activity of irradiated onions in bacterial systems. Because onion bulbs contain a considerable amount of free amino acids, we used indicator strains carrying the marker for mutagenicity other than the amino acid requirement. In this paper we describe the results on irradiated onions. We used tests with solid and liquid media, assaying for the streptomycin (SM) dependence in a strain having a tetracycline (TC)-resistance factor, as well as DNA repair tests using two sets of indicator strains.

Combined effects of radiation and inorganic reagents during irradiation on radiosensitivity of bacterial cells.

The combined effects of inorganic reagents and radiation on the inactivation of E. coli in the resting state were studied. Among these reagents halides such as NaCI, KCI, KBr and KI were found to have a considerable synergistic action to radiation. Temperature effect on the halide action during irradiation was not observed, but removal of oxygen from halide solutions increased the radiosensitivity of cells. Combined effects of radiation and some other inorganic reagents were also investigated. Heavy metal salts and hydrogen peroxide were synergistic, nitrates and sulfates having no influence or a slightly protective action. Barium chloride and calcium chloride were protective in lower concentrations and synergistic in higher concentrations. These synergistic actions of inorganic reagents except ferric salts were observed during irradiation, but not after the irradiation.

Inactivation of phage phiX 174 by accelerated ions enhanced delta-ray effect by air layer in front of the samples. [. cap alpha. particles and neon ions]

Different inactivation rates of phage φX 174 were observed between two irradiation methods for charged particles. In method EA, phage particles were spread on a thin film and exposed to air during irradiation. In method CF, the phage sample was covered with a thin polycarbonate film to eliminate the effect of secondary electrons ejected from air in front of the sample. The apparent inactivation efficiency of primary particles determined by method EA was found to be higher than that found by method CF in the case of both α-particles and nitrogen ions. The observed increase in inactivation can be explained by the dispersed energy loss of secondary electrons produced in air as compared with those produced in polycarbonate.

Synergistic Actions of Halogenophenols on Radiation Inactivation of Microorganisms

The combined effects of radiations and halogenophenols were investigated. The activities of these reagents to increase the radiolethality during irradiation were demonstrated with E. coli and Z. soya. Some relationships between chemical structure and activity were revealed as follows at pH 6 and 8: (1) effectiveness of substituted halogen was in the order of I>Br>Cl; (2) effectiveness of the monosubstituting position on a benzene ring of halogenophenols was increased in the order of p->m->o-; (3) effectiveness increased with increasing the number of halogen atom. The halogenophenol action was also found to be considerably pH-dependent. In the case of chlorinated derivatives, the synergistic activity to increase the radiolethality was intensified on the acidic side, though bromides and iodides were more effective on the basic side.

LET EFFECTS IN MICROCOCCUS RADIODURANS IRRADIATED WITH

From view point of the study on LET effects on bacteria, log- and stationary-phase cells of M. radiodurans, an extremely radioresistant vegetative bacterium, suspended in the phosphate buffer were exposed to 26 MeV α-particles from the IPCR cyclotron. The results obtained were compared with those on γ-irradiation. On such liquid-phase irradiation, survival curves of M. radiodurans for α-particles were found exponential while they were of sigmoidal or cumulative type for γ-rays. In addition, the dose-rate effect was observed with α-bombardment, although it was not found with γ-irradiation. For a given dose and in a system where the effective volume was sufficiently small as compared with the total sample volume, the relation of the surviving fraction S to the beam intensity I was represented by an empirical equation, where t is irradiation time, q0 is D37, and k and p are constant. By means of sedimentation analysis, double-strand scissions in DNA caused by α-particles were found repairable during the post...