The alga Chlamydomonas reinhardtii UVS11 gene is responsible for cell division delay and temporal decrease in histone H1 kinase activity caused by UV irradiation

The aim of the present work was to study the possible role of the UVS11 gene of the alga Chlamydomonas reinhardtii, in regulation of the cell cycle. To characterize the defect of a uvs11 mutant in respect to DNA damage-dependent cell cycle arrest, we examined first the influence of the tubulin-destabilizing drug methyl benzimidazole-2-yl-carbamate (MBC) on inhibition of mitosis in response to UV 254nm. Then the growth and reproductive processes and activity of cyclin-dependent kinases (CDK)-like kinases during the cell cycle of C. reinhardtii were investigated. In both, the wild type and the uvs11 mutant strain were compared under standard conditions and after DNA damage caused by UV 254nm. We assume the green alga C. reinhardtii possesses control mechanisms allowing to stop the cell cycle progression before mitosis in response to DNA damage. The results indicate that the uvs11 mutant is not able to stop the cell cycle after UV irradiation. We suggest that a product of the UVS11 gene affects cell response to DNA damage and influences a decrease in histone H1 kinase activity.     

Isolation and physiological characterization of mitomycin C-sensitive/UV-sensitive mutants in Bacteroides fragilis

Mutants of Bacteroides fragilis sensitive to mitomycin C were isolated after mutagenesis with ethyl methane sulphonate. One mutant (MTC25) was markedly sensitive to mitomycin C but was unaffected as regards UV sensitivity; another mutant (UVS9) was sensitive to UV radiation but was only moderately sensitive to mitomycin C. Caffeine decreased the survival after UV-irradiation of the wild-type, MTC25 and UVS9 strains by the same relative amount. Aerobic liquid holding recovery occurred in each of the three strains. The MTC25 and UVS9 mutants showed reduced host cell phage reactivation. The wild-type, MTC25 and UVS9 strains all showed UV- and H2O2-induced phage reactivation. The physiological characterization of the MTC25 and UVS9 mutants indicates that it is possible to differentiate between mechanisms for the repair of mitomycin C- and UV-induced DNA damage in B. fragilis.     

Are Freshwater Mixotrophic Ciliates Less Sensitive to Solar Ultraviolet Radiation than Heterotrophic Ones?1

We tested whether mixotrophic ciliates are more resistant to solar ultraviolet radiation (UVR) than heterotrophic ones because symbiotic algae can provide self-shading by cell matter absorption and eventually by direct UV screening from mycosporine-like amino acids (MAAs). Sensitivity of a natural assemblage to solar radiation was tested in experiments in the original lake and in a more UV transparent alpine lake after transplantation of the ciliates. In both lakes, the assemblage was exposed either to full sunlight, to photosynthetically active radiation only, or kept in the dark. In each lake, exposure was for 5 h at the surface and at the depth corresponding to the 10% attenuation depth at 320 nm. Overall, when the assemblage was exposed to surface UVR, only one out of four dominant mixotrophic ciliates, Vorticella chlorellata, was more resistant than heterotrophic species. The higher UV resistance in V. chlorellata was related to the presence of MAAs and the high percentage of ciliate volume occupied by algal symbionts. Our results indicate that effects of UVR were species-specific and depended on efficient screening of these wavelengths, but also on the depth preference of the ciliates and thus, on their previous exposure history to UVR.     

产毒与不产毒铜绿微囊藻对模拟酸雨及紫外辐射的生理响应

为了比较研究酸雨与紫外辐射对淡水水体常见藻华蓝藻的生理学影响,选取铜绿微囊藻(Microcystis aeruginosa)产毒(FACHB-905)与不产毒(FACHB-469)株系作为实验材料,通过人工模拟酸雨,研究了不同p H处理后2藻株的光合生理变化以及对紫外辐射的敏感性的异同。实验设置3个p H梯度,p H7.10为对照组(正常培养基培养的藻体),两模拟酸雨处理组(p H5.65和p H4.50);两种辐射处理,可见光处理(PAR)以及全波长辐射处理(PAB)。研究结果表明,905藻株细胞粒径在各p H处理下都要显著高于469藻株,模拟酸雨处理显著降低了两藻株细胞的平均粒径及体积,但叶绿素含量显著提高;酸雨处理同时也引起细胞死亡率的增加,表现为藻体有效光化学效率显著降低,生长速率显著受到抑制,低p H下呈负增长,且这种抑制程度在469下更为显著。高的可见光以及紫外辐射处理,使两株系有效光化学效率随p H的降低而呈降低趋势,其中469藻株降低至更低的水平,且高光辐射以及紫外诱导的抑制率要显著高于905藻体,这可能与469藻株较低的光保护色素有关(较低的类胡萝卜素以及紫外吸收物质)。在未来全球变化背景下,不同种类的浮游植物对环境变化的响应及适应能力不同,可改变水体的群落结构和种群丰度,铜绿微囊藻905较469较强的耐受酸雨以及紫外辐射的能力,可能会使该株系在竞争力上占据优势。     

Interaction of COP1 and UVR8 regulates UV‐B‐induced photomorphogenesis and stress acclimation in Arabidopsis

The ultraviolet‐B (UV‐B) portion of the solar radiation functions as an environmental signal for which plants have evolved specific and sensitive UV‐B perception systems. The UV‐B‐specific UV RESPONSE LOCUS 8 (UVR8) and the multifunctional E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) are key regulators of the UV‐B response. We show here that uvr8‐null mutants are deficient in UV‐B‐induced photomorphogenesis and hypersensitive to UV‐B stress, whereas overexpression of UVR8 results in enhanced UV‐B photomorphogenesis, acclimation and tolerance to UV‐B stress. By using sun simulators, we provide evidence at the physiological level that UV‐B acclimation mediated by the UV‐B‐specific photoregulatory pathway is indeed required for survival in sunlight. At the molecular level, we demonstrate that the wild type but not the mutant UVR8 and COP1 proteins directly interact in a UV‐B‐dependent, rapid manner in planta. These data collectively suggest that UV‐B‐specific interaction of COP1 and UVR8 in the nucleus is a very early step in signalling and responsible for the plant's coordinated response to UV‐B ensuring UV‐B acclimation and protection in the natural environment.     

Induction and repair of DNA strand breaks in Bacteroides fragilis

Alkaline sucrose gradient sedimentation was used to establish whether strand breakage and repair take place in the DNA of UV-irradiated Bacteroides fragilis during the removal of pyrimidine dimers. A B. fragilis wild-type strain and two of its repair mutants, a mitomycin C sensitive mutant (MTC25) having wild-type levels of UV survival, and a UV-sensitive, mitomycin C sensitive mutant (UVS9), were investigated. Under anaerobic conditions, far-UV irradiation induced metabolically regulated strand breakage and resynthesis in the wild-type strain, but this was markedly reduced in both the MTC25 and UVS9 mutants. Approximately half of the strand breaks generated by the various strains were rejoined during further holding in buffer. Under replicating conditions, complete repair of strand breaks in the wild type was observed. Caffeine treatment under anaerobic conditions caused direct DNA strand breakage in B. fragilis cells but did not inhibit UV-induced breakage or repair.     

Effects of solar UV radiation on morphology and photosynthesis of filamentous cyanobacterium Arthrospira platensis

To study the impact of solar UV radiation (UVR) (280 to 400 nm) on the filamentous cyanobacterium Arthrospira (Spirulina) platensis, we examined the morphological changes and photosynthetic performance using an indoor-grown strain (which had not been exposed to sunlight for decades) and an outdoor-grown strain (which had been grown under sunlight for decades) while they were cultured with three solar radiation treatments: PAB (photosynthetically active radiation [PAR] plus UVR; 280 to 700 nm), PA (PAR plus UV-A; 320 to 700 nm), and P (PAR only; 400 to 700 nm). Solar UVR broke the spiral filaments of A. platensis exposed to full solar radiation in short-term low-cell-density cultures. This breakage was observed after 2 h for the indoor strain but after 4 to 6 h for the outdoor strain. Filament breakage also occurred in the cultures exposed to PAR alone; however, the extent of breakage was less than that observed for filaments exposed to full solar radiation. The spiral filaments broke and compressed when high-cell-density cultures were exposed to full solar radiation during long-term experiments. When UV-B was screened off, the filaments initially broke, but they elongated and became loosely arranged later (i.e., there were fewer spirals per unit of filament length). When UVR was filtered out, the spiral structure hardly broke or became looser. Photosynthetic O(2) evolution in the presence of UVR was significantly suppressed in the indoor strain compared to the outdoor strain. UVR-induced inhibition increased with exposure time, and it was significantly lower in the outdoor strain. The concentration of UV-absorbing compounds was low in both strains, and there was no significant change in the amount regardless of the radiation treatment, suggesting that these compounds were not effectively used as protection against solar UVR. Self-shading, on the other hand, produced by compression of the spirals over adaptive time scales, seems to play an important role in protecting this species against deleterious UVR. Our findings suggest that the increase in UV-B irradiance due to ozone depletion not only might affect photosynthesis but also might alter the morphological development of filamentous cyanobacteria during acclimation or over adaptive time scales.     

A DNA-damage-induced cell cycle checkpoint in Arabidopsis

Although it is well established that plant seeds treated with high doses of gamma radiation arrest development as seedlings, the cause of this arrest is unknown. The uvh1 mutant of Arabidopsis is defective in a homolog of the human repair endonuclease XPF, and uvh1 mutants are sensitive to both the toxic effects of UV and the cytostatic effects of gamma radiation. Here we find that gamma irradiation of uvh1 plants specifically triggers a G(2)-phase cell cycle arrest. Mutants, termed suppressor of gamma (sog), that suppress this radiation-induced arrest and proceed through the cell cycle unimpeded were recovered in the uvh1 background; the resulting irradiated plants are genetically unstable. The sog mutations fall into two complementation groups. They are second-site suppressors of the uvh1 mutant's sensitivity to gamma radiation but do not affect the susceptibility of the plant to UV radiation. In addition to rendering the plants resistant to the growth inhibitory effects of gamma radiation, the sog1 mutation affects the proper development of the pollen tetrad, suggesting that SOG1 might also play a role in the regulation of cell cycle progression during meiosis.     

Lethal and mutagenic effects of radiation and alkylating agents on two strains of mouse L5178Y cells

In previous studies, the two closely related strains of L5178Y (LY) mouse lymphoma cells, LY-R and LY-S, have been shown to differ in their sensitivity to UV and ionizing radiation. Thus, in comparison to strain LY-R, strain LY-S has been found to be more sensitive to the lethal effects of ionizing radiation, more resistant to the lethal effects of UV radiation, but less mutable at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus by both UV and X-radiation. In the present work, the lethal and mutagenic effects of ethyl methanesulfonate (EMS), methyl nitrosourea (MNU) and UV radiation (254 nm) were compared in the two strains. Mutability at the Na+/K+-ATPase locus as well as the HGPRT locus was determined. As previously reported, we found strain LY-S to be more resistant than strain LY-R to the lethal effects of UV radiation. In contrast, strain LY-S was more sensitive to the cytotoxic effects of the two alkylating agents. In spite of these differences in sensitivity, we found strain LY-S to be less mutable than strain LY-R by all 3 agents at the HGPRT locus. At the Na+/K+-ATPase locus, strain LY-S was also less mutable than strain LY-R by equal concentrations of EMS and UV radiation and by equitoxic concentrations of MNU. However, the difference between the strains was much more pronounced at the HGPRT locus than at the Na+/K+-ATPase locus. We have suggested that the interaction of unrepaired lesions in strain LY-S tends to cause an excess of deletions and multilocus effects, which in turn result in a locus-dependent decrease in the recovery of viable LY-S mutant cells.     

Relation between repair mechanisms and induced mitotic recombination after UV irradiation, in the yeast Schizosaccharomyces pombe. Effects of caffeine

Summary Two different pathways A and 1 are known to control the repair of UV lesions in the yeast Schizosaccharomyces pombe. The relation between the UV-induced intergenic mitotic crossing over (MCO) and the repair of prelethal lesions controlled by these pathways were studied in the following strains: UVS1,₁/UVS1,₁, where pathway A acts; UVSA/UVSA where pathway 1 acts, UVS⁺/UVS⁺ (wild type) and UVS1A/UVS1A (double mutant). The analysis of the survival and MCO induction curves, and the comparison, as a function of the dose and as a function of survival, of the MCO induction curves corresponding to the different strains, show that the repair pathway 1 controls a mechanism involving recombination, and that the repair pathway A controls a mechanism which removes prerecombinational lesions. Studies were done with UVS1,₁/UVS1,₁ cells in different physiological conditions affecting the repair efficiency of prelethal lesions (irradiation during the logarithmic growth phase, liquid holding). In all cases the more efficient the repair of prelethal lesions is, the smaller is the recombination inducibility. This is expected if pathway A controls an excision repair mechanism.The effect of the repair inhibitor, caffeine, was studied. It inhibits only the repair of UV prelethal lesions controlled by pathway 1. The involvement of recombination in the repair of UV lesions in UVS⁺/UVS⁺ and UVSA/UVSA cells is also shown by the fact that the sensitization to the lethal effect of UV by caffeine in these strains is correlated with a decrease in UV MCO inducibility. Caffeine has no effect either on the UV survival, or on the MCO inducibility in UVS1,₁/UVS1,₁ cells. It is concluded that it inhibits the recombinational repair pathway and not the excision repair pathway.The MCO induction observed in UVS1/UVS1 and UVS1A/UVS1A cells could be due to the presence of a second recombinational pathway, not sensitive to caffeine. At least a fraction of the prerecombinational lesions would not be prelethal, and they are repairable by the excision repair mechanism.     

General characteristics, molecular and genetic analysis of two new UV-sensitive mutants of Chlamydomonas reinhardtii

Two new UV-sensitive mutants of Chlamydomonas, UVS10 and UVS11, were isolated. Both behave as single nuclear mutations. UVS10 was mapped to linkage group I. UVS11 is a separate, unlinked mutation but has not yet been located to a specific linkage group. Both mutants are proficient in the excision of pyrimidine dimers from nuclear DNA. The survival of UV-irradiated UVS11 is increased when plated in the presence of 1.5 mM caffeine, similar to wild-type. Caffeine has no effect on the survival of UV-irradiated UVS10. UV-irradiated UVS11 frequently divides at least once before dying, in contrast to UVS10 or wild-type. UVS11 also exhibits a much increased frequency of mutation to streptomycin resistance after UV irradiation.     

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.     

Mechanism of inhibition of human natural killer activity by ultraviolet radiation

Ultraviolet radiation (UVR) has been shown to inhibit various immune functions in vivo and in vitro. We have confirmed that UVR inhibits human natural killer (NK) activity in vitro and have shown that UVR inhibits human ADCC. In this report, the mechanism by which UVR inhibits NK function was investigated by analyzing the stage at which the inhibiting activity occurs and the ability of the NK cells to release cytotoxic factors previously shown to be involved in CMC. Single cell assays in Agarose revealed that inhibition of NK activity was localized at the postbinding lethal hit stage rather than the initial recognition or binding stage of lysis. We then examined whether UV-treated cells were able to release cytotoxic factors after stimulation with target cells. As expected, stimulated cells released cytotoxic factors, yet, surprisingly, these factors were also released in the absence of stimulator cells. The spontaneous release was detectable in the supernatants as early as 30 min after UV irradiation. The lytic material examined in 48- to 72-hr viability assays was not NK specific, because lysis was obtained with a wide range of NK sensitive and resistant target cells. These results demonstrate that UVR does not alter the capacity of the cells to secrete cytotoxic material, but in fact enhances its release. Several possible mechanisms are proposed to explain the UVR-induced NK inhibition.     

Improvement of the basidiomyceteCoprinus sp.

Coprinus sp. C-1 (obtained from uranium mines) was subjected to improvement procedures with the aim of preparing a strain that could degrade cellulose in the straw substrate more rapidly and effectively. The original C-1 strain was highly resistant to UV and X radiation but it was rather sensitive to tris(2-chloroethyl)amine, the effect of which increased when applying simultaneously compounds reacting with mercapto groups of some enzymes. The mutants obtained synthesized during the same interval by up to 94% more N compounds than the original strain the rate of cellulose degradation increasing by about 40%. In certain mutants the content of some essential amino acids simultaneously increased by up to 110%.     

Effect of UV light disinfection on antibiotic-resistant coliforms in wastewater effluents.

Total coliforms and total coliforms resistant to streptomycin, tetracycline, or chloramphenicol were isolated from filtered activated sludge effluents before and after UV light irradiation. Although the UV irradiation effectively disinfected the wastewater effluent, the percentage of the total surviving coliform population resistant to tetracycline or chloramphenicol was significantly higher than the percentage of the total coliform population resistant to those antibiotics before UV irradiation. This finding was attributed to the mechanism of R-factor-mediated resistance to tetracycline. No significant difference was noted for the percentage of the surviving total coliform population resistant to streptomycin before or after UV irradiation. Multiple drug resistance patterns of 300 total coliform isolates revealed that 82% were resistant to two or more antibiotics. Furthermore, 46% of these isolates were capable of transferring antibiotic resistance to a sensitive strain of Escherichia coli.     

Extremophiles: radiation resistance microbial reserves and therapeutic implications

Micro‐organisms with the ability to survive in extreme environmental conditions are known as ‘extremophiles’. Currently, extremophiles have caused a sensation in the biotechnology/pharmaceutical industries with their novel compounds, known as ‘extremolytes’. The potential applications of extremolytes are being investigated for human therapeutics including anticancer drugs, antioxidants, cell cycle‐blocking agents, anticholesteric drugs, etc. It is hypothesized that the majority of ultraviolet radiation (UVR)‐resistant micro‐organisms can be used to develop anticancer drugs to prevent skin damage from UVR. The metabolites from UVR‐resistant microbes are a great source of potential therapeutic applications in humans. This article aims to discuss the potentials of extremolytes along with their therapeutic implications of UVR extremophiles. The major challenges of therapeutic development using extremophiles are also discussed.     

Effects of Solar UV Radiation on Morphology and Photosynthesis of Filamentous Cyanobacterium Arthrospira platensis

To study the impact of solar UV radiation (UVR) (280 to 400 nm) on the filamentous cyanobacterium Arthrospira (Spirulina) platensis, we examined the morphological changes and photosynthetic performance using an indoor-grown strain (which had not been exposed to sunlight for decades) and an outdoor-grown strain (which had been grown under sunlight for decades) while they were cultured with three solar radiation treatments: PAB (photosynthetically active radiation [PAR] plus UVR; 280 to 700 nm), PA (PAR plus UV-A; 320 to 700 nm), and P (PAR only; 400 to 700 nm). Solar UVR broke the spiral filaments of A. platensis exposed to full solar radiation in short-term low-cell-density cultures. This breakage was observed after 2 h for the indoor strain but after 4 to 6 h for the outdoor strain. Filament breakage also occurred in the cultures exposed to PAR alone; however, the extent of breakage was less than that observed for filaments exposed to full solar radiation. The spiral filaments broke and compressed when high-cell-density cultures were exposed to full solar radiation during long-term experiments. When UV-B was screened off, the filaments initially broke, but they elongated and became loosely arranged later (i.e., there were fewer spirals per unit of filament length). When UVR was filtered out, the spiral structure hardly broke or became looser. Photosynthetic O₂ evolution in the presence of UVR was significantly suppressed in the indoor strain compared to the outdoor strain. UVR-induced inhibition increased with exposure time, and it was significantly lower in the outdoor strain. The concentration of UV-absorbing compounds was low in both strains, and there was no significant change in the amount regardless of the radiation treatment, suggesting that these compounds were not effectively used as protection against solar UVR. Self-shading, on the other hand, produced by compression of the spirals over adaptive time scales, seems to play an important role in protecting this species against deleterious UVR. Our findings suggest that the increase in UV-B irradiance due to ozone depletion not only might affect photosynthesis but also might alter the morphological development of filamentous cyanobacteria during acclimation or over adaptive time scales.     

Effects of UV-B radiation on the structural and physiological diversity of bacterioneuston and bacterioplankton

The effects of UV radiation (UVR) on estuarine bacterioneuston and bacterioplankton were assessed in microcosm experiments. Bacterial abundance and DNA synthesis were more affected in bacterioplankton. Protein synthesis was more inhibited in bacterioneuston. Community analysis indicated that UVR has the potential to select resistant bacteria (e.g., Gammaproteobacteria), particularly abundant in bacterioneuston.     

Visual modelling suggests a weak relationship between the evolution of ultraviolet vision and plumage coloration in birds

Birds have sophisticated colour vision mediated by four cone types that cover a wide visual spectrum including ultraviolet (UV) wavelengths. Many birds have modest UV sensitivity provided by violet‐sensitive (VS) cones with sensitivity maxima between 400 and 425 nm. However, some birds have evolved higher UV sensitivity and a larger visual spectrum given by UV‐sensitive (UVS) cones maximally sensitive at 360–370 nm. The reasons for VS–UVS transitions and their relationship to visual ecology remain unclear. It has been hypothesized that the evolution of UVS‐cone vision is linked to plumage colours so that visual sensitivity and feather coloration are ‘matched’. This leads to the specific prediction that UVS‐cone vision enhances the discrimination of plumage colours of UVS birds while such an advantage is absent or less pronounced for VS‐bird coloration. We test this hypothesis using knowledge of the complex distribution of UVS cones among birds combined with mathematical modelling of colour discrimination during different viewing conditions. We find no support for the hypothesis, which, combined with previous studies, suggests only a weak relationship between UVS‐cone vision and plumage colour evolution. Instead, we suggest that UVS‐cone vision generally favours colour discrimination, which creates a nonspecific selection pressure for the evolution of UVS cones.     

Ultraviolet-sensitive vision in long-lived birds

Long-term exposure to ultraviolet (UV) light generates substantial damage, and in mammals, visual sensitivity to UV is restricted to short-lived diurnal rodents and certain marsupials. In humans, the cornea and lens absorb all UV-A and most of the terrestrial UV-B radiation, preventing the reactive and damaging shorter wavelengths from reaching the retina. This is not the case in certain species of long-lived diurnal birds, which possess UV-sensitive (UVS) visual pigments, maximally sensitive below 400 nm. The Order Psittaciformes contains some of the longest lived bird species, and the two species examined so far have been shown to possess UVS pigments. The objective of this study was to investigate the prevalence of UVS pigments across long-lived parrots, macaws and cockatoos, and therefore assess whether they need to cope with the accumulated effects of exposure to UV-A and UV-B over a long period of time. Sequences from the SWS1 opsin gene revealed that all 14 species investigated possess a key substitution that has been shown to determine a UVS pigment. Furthermore, in vitro regeneration data, and lens transparency, corroborate the molecular findings of UV sensitivity. Our findings thus support the claim that the Psittaciformes are the only avian Order in which UVS pigments are ubiquitous, and indicate that these long-lived birds have UV sensitivity, despite the risks of photodamage.