Mutants of the phototrophic bacteria Rhodobacter sphaeroides sensitive to the mutagenic action of long-wave ultraviolet light

The mutagenic action of near ultraviolet (NUV, greater than or equal to 280) nm) on purple phototrophic soil bacteria Rhodobacter sphaeroides: wild strain 2R and 12 mutants obtained earlier sensitive to UV derivates (UVS) was investigated. The mutagenic action of NUV was measured by induction of resistance to tetracycline (Tet) and nalidixic acid (Nal) and reversion of pigment mutants to wild-type phenotype. The NUV light induces the mutations of resistance to Nal and Tet in wild-type strain 2R; the UVS mutants differed greatly in their NUV-induced mutability. Three UVS mutants were characterized by greatly increased mutability in all analysed loci; slight mutability was found in seven mutants. On the basis of the data obtained it has been concluded that the UVS mutants R. sphaeroides can be used as test organisms in estimation of mutagenic activity of NUV. The molecular mechanisms and genetic control of NUV-induced mutagenesis are discussed.     

A photosynergistic lethal effect in the irradiation of yeasts with long-wave ultraviolet and visible light

A lethal synergistic effect which is expressed as the nonadditive summing of the damaging effect of each irradiation separately has been found during the investigation of combined action of longwave ultraviolet (UV) rays (337 nm or 365 nm) and visible light (400-600 nm) on the yeast cells. Based on the data on different mechanisms of lethal effect of longwave UV and visible light, it has been suggested that the basis of the photosynergistic effect is the mutual intensification of the photo-destructive processes occurring in different intracellular structures and processes induced by different endogenous sensitizers.     

Effect of long-wave ultraviolet light (313 nm) on the survivability and respiration of Candida utilis yeasts

Irradiation of Candida utilis with near-UV (313 nm) was found to inhibit respiration; the degree of the inhibition correlated with the number of killed cells. Irradiation of the yeast mitochondria inhibited the activity of succinate oxidase; the dependence of the inhibition on the dose of near-UV (313 nm) was close to the dose dependence of the photoinhibition of respiration in whole cells. The action spectrum for the inhibition of the activity of succinate oxidase was recorded; it corresponded to the absorption spectrum of ubiquinone isolated from the yeast cells. The data obtained suggest that ubiquinone is a target molecule in the effects of inhibition of respiration and death of yeast cells induced with near-UV (313 nm).     

Delayed light action spectra of several algae in visible and ultraviolet light

Action spectra for delayed light production by several algae were determined from 250 to 750 mµ incident light. In the visible portion of the spectrum the action spectra resemble those reported by previous workers for photosynthesis and light emission. Blue-green algae had a maximum at 620 mµ, red algae at 550 mµ, whereas green and brown algae have action spectra corresponding to chlorophyll and carotenoid absorption. In the ultraviolet portion of the spectrum delayed light is emitted by algae down to 250 mµ incident light. The action spectra of the different algae are not alike in the ultraviolet portion of the spectrum. This indicates that pigments other than chlorophyll must be sensitizing or shielding the algae in the ultraviolet region.     

The action of ultraviolet light on the patterns of banding induced by restriction endonucleases in human chromosomes

The irradiation of metaphase spreads of human cells with ultraviolet (UV) light blocked the chromosome banding induced by Alu I, Mbo I, Dde I, Hinf I, Hae III, and Rsa I restriction endonucleases. At 13 J/m² there was moderate inhibition of the nuclease action, which was detected as an increase in the stain intensity of chromosomes (Alu I, Mbo I, Dde I, Rsa I) or as a change in the banding pattern (Hinf I, Hae III). At 70–300 J/m² the UV-induced blockage was complete; the chromosomes showed no banding, and stain intensity was similar to that of control slides incubated with buffer. — BrdU substitution and the irradiation of BrdU-substituted chromosomes with 313 nm light at 1800–15000 J/m² did not block the action of restriction nucleases. On the other hand, UV irradiation of BrdU-substituted chromosomes inhibited the action of restriction enzymes at the same fluences that blocked the nuclease action in unsubstituted chromosomes. The data indicate that DNA-protein crosslinkage is the factor inhibiting DNA extraction and chromosome banding.     

长波紫外线照射对花背蟾蜍肾脏结构损伤

为研究长波紫外线对花背蟾蜍(Buforaddei)肾脏的损伤,用波长为365nm的长波紫外线(UVA)以352μW.cm-2的辐射量对花背蟾蜍亚成体进行150、300和450min的连续照射,分别在照射后立即、3、6、9、12和15d取材,常规石蜡切片。结果表明:UVA照射后,3组不同照射时间的花背蟾蜍肾脏整体结构基本完整,但均出现肾小管管壁破裂,管径显著缩小,肾小囊消失,而300min照射组的损伤则极为明显,其后依次为450min照射组与150min照射组,300与450min照射组的肾小体塌陷程度较150min照射组更为严重;经15d的恢复,虽出现明显好转,但大多指标仍与对照组间存在极显著性差异;UVA对花背蟾蜍肾脏有着不可忽视的损伤,虽然具有一定的自我修复的能力,但在野外,紫外辐射的增强和植被的减少可导致两栖类遭受过度的紫外辐射,进而引起两栖类种群的衰减。     

The action of ultraviolet radiation on yeast catalase

The effect of prolonged UV irradiation (mostly 2537 A) on the catalase activity of an aqueous yeast suspension was divisible into 4 periods. First, the period during which the cells lost their ability to form colonies, but during which no change in catalase activity was noted. Second, the period during which a considerable rise in catalase activity (Euler effect) occurred. The Euler effect was accompanied by enzyme alteration as shown by the simultaneous decrease in the activation energy of the enzyme-substrate system. However, during the initial phase of this period, as the catalase activity of the suspension began to increase, the activation energy rose to a transient level higher even than that characterizing the unaltered enzyme. Heat accelerated the rate of alteration when applied either during or after the irradiation; the activation energy for the over-all alteration reaction was 24 kcal., a value close to that recorded previously for alteration induced by chemical agents. Nevertheless, the rate-limiting step appeared to be different in the two cases. A model of these events was presented in which the primary photochemical action was on the site at which catalase is located within the cell. Third, a rather long period during which irradiation led to no diminution in the catalase activity of the maximally active suspension. This protection effect was duplicated in intro by a model crystalline catalase-KNA system, or by adding either ribonuclease digestion products of RNA or adenine to a catalase solution prior to irradiation. Evidence was adduced that the protection effect was not a simple screening, but involved some sort of interaction between the enzyme and the nitrogenous components of RNA, an interaction which must likewise occur within the cell. Alteration induced by CHCl₃ did not eliminate the protection effect, but that by butanol did. The onset of photoinactivation was due to modification of protein structure, not of RNA. Fourth, the period of photoinactivation of the intracellular enzyme, which was quite similar to that of the crystalline enzyme in vitro.     

Use of action spectra for identifying molecular targets and mechanisms of action of solar ultraviolet light

The use of action spectra in the elucidation of the mechanisms of biological action of solar ultraviolet radiation that reaches the surface of the earth is reviewed, and precautions in the preparation and interpretation of such action spectra are discussed. Original experiments are also described which show correlations between lethality and DNA breakage caused by monochromatic solar ultraviolet (UV) wavelengths in Escherichia coli and Bacillus subtilis , which may constitute evidence for an important biological role of DNA breaks leading to lethality in these microorganisms.