Both solar UVA and UVB radiation impair conidial culturability and delay germination in the entomopathogenic fungus Metarhizium anisopliae.

The entomopathogenic hyphomycete Metarhizium anisopliae has been used in programs of agricultural pest and disease vector control in several countries. Exposure to simulated solar radiation for a few hours can completely inactivate the conidia of the fungus. In the present study we determined the effect of exposures to full-spectrum sunlight and to solar ultraviolet A radiation at 320-400 nm (UVA) on the conidial culturability and germination of three M. anisopliae strains. The exposures were performed in July and August 2000 in Logan, UT. The strains showed wide variation in tolerance when exposed to full-spectrum sunlight as well as to UVA sunlight. Four-hour exposures to full-spectrum sunlight reduced the relative culturability by approximately 30% for strain ARSEF 324 and by 100% for strains ARSEF 23 and 2575. The relative UV sensitivity of the two more sensitive strains was different under solar UV from that under ultraviolet B radiation at 280-320 nm (UVB) in the laboratory. Four-hour exposures to solar UVA reduced the relative culturability by 10% for strain ARSEF 324, 40% for strain ARSEF 23 and 60% for strain ARSEF 2575. Exposures to both full-spectrum sunlight and UVA sunlight delayed the germination of the surviving conidia of all three strains. These results, in addition to confirming the deleterious effects of UVB, clearly demonstrate the negative effects of UVA sunlight on the survival and germination of M. anisopliae conidia under natural conditions. The negative effects of UVA in sunlight also emphasize that the biological spectral weighting functions for this fungus must not neglect the UVA wavelengths.     

Effects of UVB irradiance on conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae: a study of reciprocity and recovery

We tested the effects of irradiances of 920 and 1200 mW m-2 (weighted irradiance) on the conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae. The conidia were exposed to the two irradiances for 1, 2, 4, 6, 7 or 8 h. Increased exposure decreased relative percent culturability. The inactivation provoked by the irradiance of 1200 mW m-2 was higher than for the 920 mW m-2, with a reduction in the 50% lethal time (LT50) from 6 h 40 min to 4 h 26 min. Reciprocity was not observed when conidia in water suspension and germinants in different stages of the germinative process were exposed to a 17.3 kJ m-2 total dose at both irradiance levels. Although nonreciprocity was observed in all situations, its magnitude varied as a function of metabolic state and/or cell-cycle phase in which the conidia were at the exposure time. The least difference between the effects of the two irradiance levels was observed when nongerminating conidia in suspension were exposed, and the greatest was observed when conidia were exposed during an advanced germination phase. Doses of 6.6 and 17.3 kJ m-2 supplied through the two irradiance levels delayed the germination of the surviving conidia. At both doses, delay was greater during exposure to the higher irradiance. Nonreciprocity was higher for the 17.3 kJ m-2 dose. Nonreciprocity magnitude, in addition to depending on the conidial physiological state, also depended on dose. The results demonstrate the importance of evaluating the impact of the increase in irradiance during the different stages of the fungal life cycle, especially during the stages which are more sensitive to UV, and not simply in dormant conidia.     

Aromatic polyketide production in Cordyceps indigotica, an entomopathogenic fungus, induced by exposure to a histone deacetylase inhibitor

Cultivation of Cordyceps indigotica, an entomopathogenic fungus, in the presence of suberoyl bis-hydroxamic acid (an HDAC inhibitor) greatly activated its polyketide synthesis apparatus to afford six novel aromatic polyketides, indigotides C-F (1-4), 13-hydroxyindigotide A (5), and 8-O-methylindigotide B (6). The structures of these compounds were determined by NMR spectroscopic analyses. Among the compounds, indigotides C-E (1-3) possessed unprecedented dimeric polyketide frameworks possibly generated via a [4 + 2] cycloaddition or Michael type reaction.     

Changes in matrix gene and protein expressions after single or repeated exposure to one minimal erythemal dose of solar-simulated radiation in human skin in vivo

Damage to the skin extracellular matrix (ECM) is the hallmark of long-term exposure to solar UV radiation. The aim of our study was to investigate the changes induced in unexposed human skin in vivo after single or repeated (five times a week for 6 weeks) exposure to 1 minimal erythemal dose (MED) of UV solar-simulated radiation. Morphological and biochemical analyses were used to evaluate the structural ECM components and the balance between the degrading enzymes and their physiologic inhibitors. A three-fold increase in matrix metalloproteinase 2 messenger RNA (mRNA) (P < 0.02, unexposed versus exposed) was observed after both single and repeated exposures. Fibrillin 1 mRNA level was increased by chronic exposure (P < 0.02) and unaltered by a single MED. On the contrary, a single MED significantly enhanced mRNA levels of interleukin-1alpha (IL-1alpha), IL-1beta (P < 0.02) and plasminogen activator inhibitor-1 (P < 0.05). Immunohistochemistry demonstrated a significant decrease in Type-I procollagen localized just below the dermal-epidermal junction in both types of exposed sites. At the same location, the immunodetected tenascin was significantly enhanced, whereas a slight increase in Type-III procollagen deposits was also observed in chronically exposed areas. Although we were unable to observe any change in elastic fibers in chronically exposed buttock skin, a significant increase in lysozyme and alpha-1 antitrypsin deposits on these fibers was observed. These results demonstrate the existence of a differential regulation, after chronic exposure compared with an acute one, of some ECM components and inflammatory mediators.     

Histone deacetylase inhibitor induced the production of three novel prenylated tryptophan analogs in the entomopathogenic fungus, Torrubiella luteorostrata

Suberoyl bis-hydroxamic acid (SBHA), a histone deacetylase (HDAC) inhibitor, led to significant changes in the secondary metabolism of an entomopathogenic fungus, Torrubiella luteorostrata, and induced the production of three new prenylated tryptophan analogs, luteorides A-C (1-3). The structures are characterized by the presence of an (E)-oxime group, which is an unusual functional group in natural products, and a 3-methylbuta-1,3-dienyl unit as a common substituent. The method of culturing entomopathogenic fungi in the presence of HDAC inhibitors, such as SBHA, is convenient and attractive for obtaining novel secondary metabolites.     

Tenuipyrone, a novel skeletal polyketide from the entomopathogenic fungus, Isaria tenuipes, cultivated in the presence of epigenetic modifiers

The concomitant addition of the histone deacetylase inhibitor and the DNA methyltransferase inhibitor to the culture medium of an entomopathogenic fungus, Isaria tenuipes, greatly enhanced its secondary metabolite production and led to the isolation of tenuipyrone (1), a novel polyketide with an unprecedented tetracyclic ring system bearing a spiroketal structural component, along with two known C(10)-polyketides, cephalosporolide B (2), which is a plausible biosynthetic precursor of 1, and cephalosporolide F (3).     

Dihydrobenzofurans as cannabinoid receptor ligands from Cordyceps annullata,an entomopathogenic fungus cultivated in the presence of an HDAC inhibitor

The secondary metabolite production of Cordyceps annullata, an entomopathogenic fungus, was clearly enhanced by the addition of suberoyl bis-hydroxamic acid (SBHA), a histone deacetylase (HDAC) inhibitor, to the culture medium. Four new 2,3-dihydrobenzofurans, annullatins A–D (1–4), and a new aromatic polyketide, annullatin E (5) were isolated from the culture medium, and the structures, including the absolute stereochemistries, were determined by spectroscopic analysis, vibrational circular dichroism (VCD), and chemical transformations. Annullatin A (1) exhibited potent agonistic activity toward the cannabinoid receptors CB1 and CB2. Annullatin B (2) and D (4) displayed CB1 agonistic activity and CB2 inverse agonistic activity.     

An example where orbital relaxation is an important contribution to the Fukui function

Density-functional electronic structure calculations are performed on the molecules Cr2(hpp)4, Mo2(hpp)4, and W2(hpp)4, where the bridging ligand, hpp, is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine. The calculated electronic densities are used to determine the Fukui functions. These molecules are unique not only in their ability as electron donors but also because orbital relaxation plays a decisive role in their reactivity. Unlike other examples in the literature, the reactivity of these compounds cannot be expressed solely in terms of the highest occupied and lowest unoccupied Kohn-Sham orbitals but only using the Fukui function, which includes the effects of orbital relaxation.     

Highly oxidized ergosterols and isariotin analogs from an entomopathogenic fungus,Gibellula formosana,cultivated in the presence of epigenetic modifying agents

The concomitant addition of a histone deacetylase inhibitor, suberoyl bis-hydroxamic acid, and a DNA methyltransferase inhibitor, RG-108, to the culture medium of Gibellula formosana, an entomopathogenic fungus, induced a significant increase in diversity of secondary metabolites. From the culture media were isolated two new highly oxidized ergosterols, formosterols A (1) and B (2), and five new isariotin analogs, 12′-O-acetylisariotin A (4), 1-epi-isariotin A (5), and isariotins K–M (6–8), together with 22,23-epoxy-3,12,14,16-tetrahydroxyergosta-5,7-dien-11-one (named formosterol C) (3), isariotins A (9), C (10), and E (11), TK-57-164A (12), and beauvericin (13). The NMR spectra, X-ray single crystallographic diffraction, and chemical transformations revealed the structures of the two new formosterols and five new isariotins. The stereochemistry of formosterol C (3) was deduced from its spectroscopic data. The side chains of formosterols A–C (1–3) contained cis-22,23-epoxide, which is rarely present in naturally occurring sterols and triterpenes.     

Nature of the chemical bond and prediction of radiation tolerance in pyrochlore and defect fluorite compounds

The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation-anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature.     

Irradiance dependence of the He-Ne laser-induced protection against UVC radiation in E. coli strains

He-Ne laser pre-irradiation-induced protection against UVC damage was investigated in wild-type E. coli K12 strain AB1157 and its isogenic DNA repair mutant strains. At a dose of 7 kJ/m(2), pre-irradiation was observed to induce protection in recA proficient strains (AB1157 and uvrA(-) AB1886) at both the irradiances investigated (2 and 100 W/m(2)). However, at the same dose (7 kJ/m(2)), while no protection was observed at 100 W/m(2) in the recA(-) strain, some protection appeared to be there at 2 W/m(2). Mechanistic studies carried out on these strains at the two irradiances suggest that, whereas the protection observed at 100 W/m(2) is mediated by singlet oxygen, that observed at 2 W/m(2) is not. Further, the fact that protection at 100 W/m(2) was observed only in recA proficient strains suggests that it may arise due to the induction of DNA repair processes controlled by the recA gene. The latter may arise due to the oxidative stress produced by singlet oxygen generated by He-Ne laser irradiation. In contrast, the protection observed at 2 W/m(2) appears to be independent of the DNA repair proficiency of the strain.     

Letter: Silver mediated ester bond formation in the gas phase: substrate structure is important

The silver acetate cation CH(3)CO(2)Ag(2)(+) reacted with allyl iodide via C-O bond coupling to produce Ag(2)I(+) and allyl acetate, but only underwent adduct formation with methyl iodide, highlighting the importance of substrate on reactivity. DFT calculations predicted the reaction with allyl iodide to be exothermic by 0.48 eV, and suggested that intermediates in the reaction benefit from multiple interactions between the allyl and iodide moieties of allyl iodide and the two silver atoms in CH(3)CO(2)Ag(2)(+).     

Expression of a ketolase gene mediates the synthesis of canthaxanthin in Synechococcus leading to tolerance against photoinhibition, pigment degradation and UV-B sensitivity of photosynthesis

The potential of ketocarotenoids to protect the photosynthetic apparatus from damage caused by excess light and UV-B radiation was assessed. Therefore, the cyanobacterium Synechococcus was transformed with a foreign beta-carotene ketolase gene under a strong promoter leading to the accumulation of canthaxanthin. This diketo carotenoid is absent in the original strain. Most of the newly formed canthaxanthin was located in the thylakoid membranes. The endogenous beta-carotene hydroxylase was unable to interact with the ketolase. Therefore, only traces of astaxanthin were found. The transformant was treated with strong light (500 or 1200 mumol m-2 s-1) and with UV-B radiation. In contrast to a nontransformed strain the overall photosynthesis, measured as oxygen evolution, was protected from inhibition by light of 500 mumol m-2 s-1 and UV-B radiation of 6.8 W m-2. Furthermore, degradation in the light of chlorophyll and carotenoids at an irradiance of 1200 mumol m-2 s-1, which was substantial in the nontransformed control, was prevented. These results indicate that in situ canthaxanthin, which is formed at the expense of zeaxanthin and replaces this hydroxy carotenoid within the photosynthetic apparatus, is a better protectant against solar radiation. These findings are discussed on the basis of the in vitro properties such as inactivating peroxyl radicals, quenching of singlet oxygen and oxidation stability of these different carotenoid structures.     

An approach to the understanding of radiation chemistry in the condensed phase

This paper describes a purely electronic mechanism by which ≈ 20 eV excitations in condensed phases relax to lower energy states. The mechanism utilizes an “energy fission” process whereby an ionic or excitonic state splits into two lower energy states, at least one being localized. The mechanism explains not only the known rapidity of such processes but also suggests an explanation for the proportionation of the chemistry between ionic and electronically excited states.     

Arg-72 of pharaonis phoborhodopsin (sensory rhodopsin II) is important for the maintenance of the protein structure in the solubilized states

In bacteriorhodopsin (bR), Arg-82bR has been proven to be a very important residue for functional role of this light-driven proton pump. The arginine residue at this position is a super-conserved residue among archaeal rhodopsins. pharaonis phoborhodopsin (ppR; or called as "pharaonis sensory rhodopsin II") has its absorption maximum at 498 nm and acts as a sensor in the membrane of Natronobacterium pharaonis, mediating the negative phototaxis from the light of wavelength shorter than 520 nm. To investigate the role of the arginine residue (Arg-72ppR) of ppR corresponding to Arg-82bR, mutants whose Arg-72ppR was replaced by alanine (R72A), lysine (R72K), glutamine (R72Q) and serine (R72S) were prepared. These mutants were unstable in low concentrations of NaCl and lost their color gradually when the proteins were solubilized with 0.1% n-dodecyl-beta-D-maltoside. The order of instability was R72S > R72A > R72K > R72Q > the wild type. The rates of denaturation were reduced in a solution of high concentrations of monovalent anions.