An investigation into the possible light-shielding role of gas vacuoles in a planktonic blue-green alga

When the gas vacuoles of Anabaena flos-aquae Bréb. ex Born. et Flah. are collapsed, the optical properties of the alga change. While this may suggest a light-shielding role, photosynthetic measurements indicate that intact gas vacuoles reduce the light falling on the thylakoids by only 4%, or less. Intact gas vacuoles offer no protection against the lethal effects of ultraviolet light. When the alga is grown at high light intensity the gas vacuoles are fewer in number but are oriented peripherally in the cells. However, this does not markedly affect their light shielding efficiency. Spectrophotometric measurements carried out by others indicate a light shielding role by gas vacuoles in a non-planktonic blue-green alga, Nostoc muscorum Kütz., but do not give a quantitative estimate of this effect. In Anabaena no definite evidence of light-shielding is obtained by such a method. All of the experiments described were conducted with dilute algal suspensions to investigate shielding effects in individual cells. Possible self-shading effects in dense suspensions and surface water blooms require further investigation.     

Ultraviolet Inactivation of Euglena Chloroplasts: I. Effect of Light Intensity of Culture

Target numbers for ultraviolet (UV) inactivation of chloroplast replication in Euglena gracilis were about 45 when cells were grown in the dark and about 150 when grown in the light (700 or 1200 foot-candles [ft-cd]). Total cell DNA was about 25% greater in the light-grown cells.     

Association of Microcyst Formation in Spirillum itersonii with the Spontaneous Induction of a Defective Bacteriophage

Mitomycin C and ultraviolet light were found to induce the formation of microcysts in Spirillum itersonii. These forms, as well as spontaneously occurring microcysts in this species, were found to contain phage tail parts, rhapidosomes, and a granular substance not seen in normal cells. It is suggested that microcysts are formed as the result of the induction of a defective phage. The production of phage lysozyme within the cell could lead to the formation of spherical forms as the cells lose their structural mucopeptide layer. Complete virus particles were not seen, nor was any biological activity demonstrated when the induced cultures were tested against two other strains of S. itersonii. The other strains of this bacterium also formed microcysts and phage tail parts when induced with mitomycin. Attempts to isolate an organism lacking the defective phage have been unsuccessful.     

Selection of Autographa californica nuclear polyhedrosis virus for resistance to inactivation by near ultraviolet,far ultraviolet,and thermal radiation

Experiments were performed to isolate strains of Autographa californica nuclear polyhedrosis virus (Baculovirus) with inherent resistance to inactivation by far ultraviolet radiation, near ultraviolet radiation, and thermal radiation. Virus with apparently increased resistance to inactivation by near ultraviolet radiation was isolated. Virus with increased resistance to far ultraviolet radiation was not obtained. No significant differences in response to thermal radiation were observed between wild virus and virus selected for increased resistance to inactivation by this agent. Repeated selection treatment with far ultraviolet radiation and with near ultraviolet radiation resulted in the production of virus with significantly reduced virulence in comparison with wild virus. The virulence of heat-selected virus did not differ from wild virus.     

Absence of gas vesicle protein in a mutant of Anabaena flos-aquae

Filaments without gas vacuoles arose spontaneously in the gas-vacuolate alga Anabaena flos-aquae. The non-vacuolate mutant was enriched by repeated sedimentation and subsequently cloned by microsyringe transfer. No revertants have been observed. In the gas-vacuolate wild-type alga the gas vesicle protein was clearly distinguished by gel electrophoresis as one of the ten most abundant protein species present in whole cell extracts. Electrophoresis indicated that the mutant had lost the ability to synthesize the gas vesicle protein. A second mutant partially defective in production of gas vacuoles and gas vesicle protein has been isolated.Abbreviations gv gas vesicle protein - pb phycobilin - TCA trichloracetic acid     

The Influence of the Environment and Clothing on Human Exposure to Ultraviolet Light

Objection

The aim of this study is to determine the effect of clothing and the environment on human exposure to ultraviolet light.

Methods

The ultraviolet (ultraviolet A and ultraviolet B) light intensity was measured, and air quality parameters were recorded in 2014 in Beijing, China. Three types of clothing (white polyester cloth, pure cotton white T-shirt, and pure cotton black T-shirt) were individually placed on a mannequin. The ultraviolet (ultraviolet A and ultraviolet B) light intensities were measured above and beneath each article of clothing, and the percentage of ultraviolet light transmission through the clothing was calculated.

Results

(1) The ultraviolet light transmission was significantly higher through white cloth than through black cloth; the transmission was significantly higher through polyester cloth than through cotton. (2) The weather significantly influenced ultraviolet light transmission through white polyester cloth; transmission was highest on clear days and lowest on overcast days (ultraviolet A: P=0.000; ultraviolet B: P=0.008). (3) Air quality parameters (air quality index and particulate matter 2.5 and 10) were inversely related to the ultraviolet light intensity that reached the earth’s surface. Ultraviolet B transmission through white polyester cloth was greater under conditions of low air pollution compared with high air pollution.

Conclusion

Clothing color and material and different types of weather affected ultraviolet light transmission; for one particular cloth, the transmission decreased with increasing air pollution.     

Light modulation of phosphofructokinase in pea leaf chloroplasts

Chloroplastic phosphofructokinase, phosphorylase, phosphoglucomutase, and phosphoglucoisomerase in peas are light inactivated. The effect of light on phosphofructokinase is mimicked by dithiothreitol. DCMU, arsenite, and sulfite inhibit light modulation of the enzyme. No effect of light inactivation on the K_m (fructose-6-P) or pH optima of phosphofructokinase was observed.     

The Ultraviolet Light Inactivation of ΦX174 Bacteriophage at Different wave Lengths and pH's

The bacterial virus, ΦX174, which contains a single strand of DNA has been inactivated by different wave lengths of monochromatic ultraviolet light at pH 7, 2, and 12. The action spectra for inactivation at these three pH's all showed minima at 2400 A rather than at 2300 A, which is the characteristic absorption minimum of DNA. The shapes of the action spectra have been analyzed in terms of the effects of absorbed light on the pyrimidines and purines rather than the effect on nucleoprotein. In this interpretation the pyrimidines are at least 2 to 3 times more sensitive than the purines. The quantum yield for inactivation of the virus at 2650 A and pH 7 is 0.006. The quantum efficiency for quanta absorbed in the pyrimidines is 0.0085 and for the purines 0.0035. It is pointed out that action spectra for single- and double-stranded polynucleotides should have minima at different wave lengths, and that this difference may be used to distinguish between these two configurations in vivo.     

Physiological effects of the presence and absence of gas vacuoles in the blue-green alga,Microcystis aeruginosa Kuetz. emend. Elenkin

Physiological evidence was obtained for a light shielding role for gas vacuoles inMicrocystis aeruginosa Kuetz. emend. Elenkin, by comparing photosynthetic oxygen evolution, growth behaviour and pigment composition of cells with intact or collapsed gas vacuoles. The oxygen evolution rates were strongly dependent on cell concentration, a maximum rate for cells with intact gas vacuoles occurring at about 1.4×10⁹ cells/ml and for cells with collapsed gas vacuoles at about 2.5×10⁹ cells/ml. By using light saturation curves for oxygen evolution, it was estimated that at low light intensities up to 30% of the photosynthetically useable light was shielded at a cell concentration of 6×10⁸ cells/ml. Collapsing the gas vacuoles twice daily did not alter the initial growth rate of the cultures, but enabled them to reach a higher final cell density. Collapsing of gas vacuoles during growth for about four generations resulted in a lower level of all acetone soluble pigments with a greater relative reduction in carotenoids than in chlorophyll a. Collapse of the gas vacuoles does not alter the cell volume. Various optical interactions which could account for light shielding are discussed.     

Determination of Pyrimidine Dimers in Escherichia coli and Cryptosporidium parvum during UV Light Inactivation, Photoreactivation, and Dark Repair

UV inactivation, photoreactivation, and dark repair of Escherichia coli and Cryptosporidium parvum were investigated with the endonuclease sensitive site (ESS) assay, which can determine UV-induced pyrimidine dimers in the genomic DNA of microorganisms. In a 99.9% inactivation of E. coli, high correlation was observed between the dose of UV irradiation and the number of pyrimidine dimers induced in the DNA of E. coli. The colony-forming ability of E. coli also correlated highly with the number of pyrimidine dimers in the DNA, indicating that the ESS assay is comparable to the method conventionally used to measure colony-forming ability. When E. coli were exposed to fluorescent light after a 99.9% inactivation by UV irradiation, UV-induced pyrimidine dimers in the DNA were continuously repaired and the colony-forming ability recovered gradually. When kept in darkness after the UV inactivation, however, E. coli showed neither repair of pyrimidine dimers nor recovery of colony-forming ability. When C. parvum were exposed to fluorescent light after UV inactivation, UV-induced pyrimidine dimers in the DNA were continuously repaired, while no recovery of animal infectivity was observed. When kept in darkness after UV inactivation, C. parvum also showed no recovery of infectivity in spite of the repair of pyrimidine dimers. It was suggested, therefore, that the infectivity of C. parvum would not recover either by photoreactivation or by dark repair even after the repair of pyrimidine dimers in the genomic DNA.     

Photoinactivation of Ichthyrotoxin from Axenic Cultures of Prymnesium parvum Carter

The ichthyotoxin of Prymnesium parvum is inactivated by visible (400 to 510 mμ) as well as by ultraviolet light (255 mμ). The changes in the absorption spectrum of purified (pigment-free) ichthyotoxin during this process indicate that different mechanisms may be involved in the inactivation by visible or ultraviolet light. Photoinactivation is not affected by the presence of cells, cell pigments, oxygen, or glutathione.     

Effect of acriflavine on ultraviolet inactivation of Acholeplasma laidlawii

An increased sensitivity to inactivation was observed when ultraviolet light-irradiated Acholeplasma laidlawiiAn increase sensitivity to inactivation was observed when ultraviolet light-irradiated Acholeplasma laidlawii cells were plated on medium containing either acriflavine or chloramphenicol. Chloramphenicol reduced liquid holding recovery (dark repair) to about 10 percent of that in untreated irradiated cells. In acriflavine treated cells no dark repair could be observed and there was a progressive degradation of cell DNA during holding. While the primary effect of acriflavine may be to inhibit excision repair, since ultraviolet-irradiated Mycoplasma gallisepticum (cells which lack an excision repair mechanism) show a slight increase in inactivation when plated on medium containing acriflavine, the dye must also have some other effects on ultraviolet repair processes. Acriflavine treatment of A. laidlawii cells before ultraviolet irradiation has a protective effect, as seen by an increased cell survival.     

On the Mechanism of the Changes in Phenylalanine Ammonia-lyase Activity Induced by Ultraviolet and Blue Light in Gherkin Hypocotyls

Irradiation with ultraviolet light causes in the hypocotyl of dark-grown gherkin seedlings the partial conversion of trans-hydroxycinnamic acids to the cis-isomers. The trans-hydroxycinnamic acids inhibit the development of phenylalanine ammonia-lyase activity, and the transformation of these compounds to the much less inhibitory cis-isomers forms a ready explanation for the increase in phenylalanine ammonia-lyase activity in the hypocotyl of gherkin seedlings irradiated with ultraviolet light. Arguments are advanced that the increase in phenylalanine ammonia-lyase activity caused by irradiation with blue light is also (at least in part) initiated by trans-cis isomerisation of the hydroxycinnamic acids.     

Multiplicity reactivation and repair of nitrous acid-induced lesions in bacteriophage T4

Nitrous acid-induced lesions in phage T4 were shown to be efficiently repaired by multiplicity reactivation. Mutants defective in genes 32, 46, 47, x and y showed substantially less MR ² of these lesions than wild type. The gene 47 mutant, which showed the least MR of nitrous acid lesions, also showed virtually no MR of ultraviolet lesions. Mutations in genes 30, 44 and v did not affect MR of nitrous acid-induced lesions. Each of the mutations which lowered MR was shown previously to reduce recombination. Our results suggest that the gene functions employed in MR are the same functions used in genetic recombination, and, based on this, we propose a tentative recombinational model for MR.The mutants defective in genes 32, 46 and 47, which are deficient in recombination, were shown to be more sensitive to nitrous acid inactivation than wild-type phage upon single infection. Our results indicate that, in wild-type single infections, about 20% of nitrous acid-induced lethal lesions may be repaired by a recombinational post-replication form of repair.     

Assessment of the Effectiveness of Low-Pressure UV Light for Inactivation of Helicobacter pylori

Three strains of Helicobacter pylori were exposed to UV light from a low-pressure source to determine log inactivation versus applied fluence. Results indicate that H. pylori is readily inactivated at UV fluences typically used in water treatment regimens. Greater than 4-log₁₀ inactivation was demonstrated on all three strains at fluences of less than 8 mJ cm⁻².     

Light production by green plants

1. Green plants have been found to emit light of approximately the same color as their fluorescent light for several minutes following illumination. This light is about 10^–3 the intensity of the fluorescent light, about one-tenth second after illumination below saturation or 10^–6 of the intensity of the absorbed light. 2. The decay curve follows bimolecular kinetics at 6.5°C. and reaction order 1.6 at 28°C. 3. This light saturates as does photosynthesis at higher light intensities and in about the same intensity range as does photosynthesis. 4. An action spectrum for light emitted as a function of the wave length of exciting light has been determined. It parallels closely the photosynthetic action spectrum. 5. The intensity of light emission was studied as a function of temperature and found to be optimal at about 37°C. with an activation energy of approximately 19,500 calories. Two-temperature studies indicated that the energy may be trapped in the cold, but that temperatures characteristic for enzymatic reactions are necessary for light production. 6. Illumination after varying dark periods showed initial peaks of varying height depending on the preceding dark period. 7. 5 per cent CO₂ reversibly depresses the amount of light emitted by about 30 per cent. About 3 minutes are required for this effect to reach completion at room temperatures. 8. Various inhibitors of photosynthesis were tested for their effect on luminescence and were all inhibitory at appropriate concentrations. 9. Irradiation with ultraviolet light (2537A) inhibits light production at about the same rate as it inhibits photosynthesis. 10. This evidence suggests that early and perhaps later chemical reactions in photosynthesis may be partially reversible.     

Inactivation of Salmonella enterica by UV-C Light Alone and in Combination with Mild Temperatures

The aim of this investigation was to study the efficacy of the combined processes of UV light and mild temperatures for the inactivation of Salmonella enterica subsp. enterica and to explore the mechanism of inactivation. The doses to inactivate the 99.99% (4D) of the initial population ranged from 18.03 (Salmonella enterica serovar Typhimurium STCC 878) to 12.75 J ml⁻¹ (Salmonella enterica serovar Enteritidis ATCC 13076). The pH and water activity of the treatment medium did not change the UV tolerance, but it decreased exponentially by increasing the absorption coefficient. An inactivating synergistic effect was observed by applying simultaneous UV light and heat treatment (UV-H). A less synergistic effect was observed by applying UV light first and heat subsequently. UV did not damage cell envelopes, but the number of injured cells was higher after a UV-H treatment than after heating. The synergistic effect observed by combining simultaneous UV and heat treatment opens the possibility to design combined treatments for pasteurization of liquid food with high UV absorptivity, such as fruit juices.     

Inactivation of Oriented Bacteria with Polarized Ultraviolet Light

Aligned deoxyribonucleic acid (DNA) molecules exhibit a large absorption anisotropy in the ultraviolet (UV) region of the spectrum (11). Also, the UV action spectra of most bacteria resemble the absorption spectrum of DNA (23), implying that inactivation is directly proportional to the UV absorbed by the bacterial DNA. Hence, the UV sensitivity of aligned uniaxial bacteria might be anisotropic with respect to polarization of the incident UV (17, 19). Any inactivation anisotropy would depend upon the orientation of DNA within the bacteria, as well as upon the alignment of bacteria, and could provide a more sensitive indication of in vivo DNA orientation than is presently available using optical methods (5, 12-16). Using an electric field of 3.5 × 10⁶ cycles/second, samples of bacteria of strain LS-301 were aligned in a quartz cell and were irradiated with UV (λ = 2652 A) polarized perpendicular and parallel to the alignment direction. The resultant survival curves resolved no inactivation anisotropy. This result is interpreted to mean that there was insufficient bacterial DNA alignment to give a detectable anisotropy. The minimum average DNA alignment necessary to have resolved an anisotropy is calculated to be 15 per cent in an axial direction (bases perpendicular to the bacterial axis) or 30 per cent in a radial direction (bases parallel to the bacterial axis).