Photodynamic Inactivation of Conidia of the Fungi Metarhizium anisopliae and Aspergillus nidulans with Methylene Blue and Toluidine Blue

Antimicrobial photodynamic treatment (PDT) is a promising method that can be used to control localized mycoses or kill fungi in the environment. A major objective of the current study was to compare the conidial photosensitization of two fungal species (Metarhizium anisopliae and Aspergillus nidulans) with methylene blue (MB) and toluidine blue (TBO) under different incubation and light conditions. Parameters examined were media, photosensitizer (PS) concentration and light source. PDT with MB and TBO resulted in an incomplete inactivation of the conidia of both fungal species. Conidial inactivation reached up to 99.7%, but none of the treatments was sufficient to achieve a 100% fungicidal effect using either MB or TBO. PDT delayed the germination of the surviving conidia. Washing the conidia to remove unbound PS before light exposure drastically reduced the photosensitization of A. nidulans. The reduction was much smaller in M. anisopliae conidia, indicating that the conidia of the two species interact differently with MB and TBO. Conidia of green and yellow M. anisopliae mutants were less affected by PDT than mutants with white and violet conidia. In contrast to what occurred in PBS, photosensitization of M. anisopliae and A. nidulans conidia was not observed when PDT was performed in potato dextrose media.     

Quantification of Cyclobutane Pyrimidine Dimers Induced by UVB Radiation in Conidia of the Fungi Aspergillus fumigatus,Aspergillus nidulans,Metarhizium acridum and Metarhizium robertsii

Conidia are responsible for reproduction, dispersal, environmental persistence and host infection of many fungal species. One of the main environmental factors that can kill and/or damage conidia is solar UV radiation. Cyclobutane pyrimidine dimers (CPD) are the major DNA photoproducts induced by UVB. We examined the conidial germination kinetics and the occurrence of CPD in DNA of conidia exposed to different doses of UVB radiation. Conidia of Aspergillus fumigatus, Aspergillus nidulans and Metarhizium acridum were exposed to UVB doses of 0.9, 1.8, 3.6 and 5.4 kJ m⁻². CPD were quantified using T4 endonuclease V and alkaline agarose gel electrophoresis. Most of the doses were sublethal for all three species. Exposures to UVB delayed conidial germination and the delays were directly related both to UVB doses and CPD frequencies. The frequencies of dimers also were linear and directly proportional to the UVB doses, but the CPD yields differed among species. We also evaluated the impact of conidial pigmentation on germination and CPD induction on Metarhizium robertsii. The frequency of dimers in an albino mutant was approximately 10 times higher than of its green wild-type parent strain after exposure to a sublethal dose (1.8 kJ m⁻²) of UVB radiation.     

Role of Ozone in UV‐C Disinfection,Demonstrated by Comparison between Wild‐Type and Mutant Conidia of Aspergillus niger

This study aimed to investigate the tolerance of a melanized wild‐type strain of Aspergillus niger (CON1) and its light‐colored mutant (MUT1) to UV–C light and the concomitantly generated ozone. Treatments were segregated into four groups based on whether UV irradiation was used and the presence or absence of ozone: (?UV, ?O₃), (?UV, +O₃), (+UV, ?O₃) and (+UV, +O₃). The survival of CON1 and MUT1 conidia under +UV decreased as the exposure time increased, with CON1 showing greater resistance to UV irradiation than MUT1. Ozone induced CON1 conidium inactivation only under conditions of UV radiation exposure. While, the inactivation effect of ozone on MUT1 was always detectable regardless of the presence of UV irradiation. Furthermore, the CON1 conidial suspension showed lower UV light transmission than MUT1 when examined at the same concentration. Compared with the pigment in MUT1, the melanin in CON1 exhibited more potent radical‐scavenging activity and stronger UV absorbance. These results suggested that melanin protected A. niger against UV disinfection via UV screening and free radical scavenging. The process by which UV–C disinfection induces a continual decrease in conidial survival suggests that UV irradiation and ozone exert a synergistic fungicidal effect on A. niger prior to reaching a plateau.     

Conidial pigmentation is important to tolerance against solar-simulated radiation in the entomopathogenic fungus Metarhizium anisopliae

The importance of conidial pigmentation to solar UV radiation tolerance in the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, was estimated by comparing the effects of exposure to simulated solar UV radiation on the wild-type parent strain U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) Collection of Entomopathogenic Fungal Cultures (ARSEF) 23, which has dark green conidia, and three groups of color mutants with yellow, purple and white conidia. The comparisons included inactivation levels and the kinetics of germination of conidia exposed or not exposed to simulated solar UV radiation. In addition to significantly inactivating the conidia of different mutants, exposure to radiation delayed for several hours the germination of surviving conidia of the wild type and all mutants. In general, mutants with white conidia were more sensitive to simulated solar UV radiation than mutants with purple conidia, which were more sensitive than mutants with yellow conidia, which in turn were more sensitive than the green wild strain. A significant variation in tolerance to simulated solar radiation was observed among mutants within each color group, particularly among mutants with yellow conidia. Revertants with green conidia, DWR 179 and DWR 176, were obtained from the very sensitive UV mutants DWR 148 (yellow conidia) and DWR 149 (purple conidia), respectively. These revertants had levels of tolerance to simulated solar UV radiation similar to those of the wild-type ARSEF 23. This observation is strong evidence of the importance of green conidial pigmentation for tolerance to simulated solar UV radiation, a factor that could be manipulated to produce M. anisopliae strains with more tolerance to solar UV radiation.     

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.     

MYCOCHROME SYSTEM AND CONIDIAL DEVELOPMENT IN CERTAIN FUNGI IMPERFECTI

Abstract. A photoreceptor system, “mycochrome”, is involved in a blue and near UV reversible photo-reaction which in turn plays an important role in the photocontrol of conidial development in Alternaria tomato, Botrytis cinerea and Helminthosporium oryzae. Conidial development was controlled by alternating exposures to blue and near UV light with the final response being determined by the final light received. When the final light was near UV a conidium developed; when it was blue, conidiation was inhibited and a “sterile” conidiophore was formed. The effects of the two lights were alternatively reversible. Blue and near UV reversible photoreaction was also found in a light-minus-dark difference spectrum of an intracellular particulate fraction isolated from dark-grown mycelia of A. tomato, and two pigments, P_B (blue absorbing type) and P_NUV (near UV absorbing type), were contained in that photoreaction. P_B was tightly bound to the particulate fraction and P_NUV was either soluble in the cytoplasm or very loosely bound to the particulate fraction. Blue and near UV reversible photoreaction occurred only under the coexistence of P_B and P_NUV. That is, a dip in the near UV region and peak absorbance in the blue region was induced by irradiation with near UV light; however, both conditions were partially dissipated with a subsequent irradiation of blue light. These absorbance changes were revers-ibly repeated by alternating doses of blue and near UV light. When molecular oxygen was introduced after exposure to near UV light, peak absorbance in the blue region rapidly disappeared, and these absorbance changes were repeatedly reversible. Similar results were obtained by treatment with sodium hydrosulfite and molecular oxygen. Thus, it was concluded that the mycochrome system suggested in photo-conidiation was consistent with certain active substances showing blue and near UV reversible absorbance changes and caused by photooxidation reduction reaction.     

TEMPERATURE AND MYCOCHROME SYSTEM IN NEAR-UV LIGHT INDUCIBLE AND BLUE LIGHT REVERSIBLE PHOTOINDUCTION OF CONIDIATION IN Alternaria tomato*

Abstract— When dark-grown colonies were exposed to near-UV light, conidiophore formation was induced, and conidia developed during a subsequent dark period. Simultaneous exposure to near-UV and blue light inhibited induction of conidiation. The inductive effect of near-UV light irradiation was greatly enhanced by treating colonies with low temperatures for 4 h during the 2nd-6th hour of incubation in the dark following inductive irradiation: the enhancement was greatest at 21^°C. The extent of inhibition by blue light increased with the temperature between 10 and 28^°C. This diminution by low temperature was greatest when colonies previously kept at a low temperature were exposed to inductive irradiation: the longer the duration between inductive irradiation and temperature treatment, the lower the diminution. Higher fluences of blue light were required to suppress conidial induction at lower temperature. Thus, it is evident that the inductive effect of near-UV light irradiation on conidiation and the suppressive effect of blue light irradiation are each responsive to different temperatures applied at different times.     

Visible-to-UV Photon Upconversion: Recent Progress in New Materials and Applications

Ultraviolet (UV, λ<400 nm) light is essential for various photochemical reactions, but its intensity in the solar spectrum is very low, and light sources that artificially generate high-energy UV light are inefficient and environmentally unfriendly. A solution to this problem is photon upconversion (UC) from visible (vis, λ>400 nm) light to UV light. Among several mechanisms, UC based on triplet-triplet annihilation (TTA-UC) in particular has made remarkable progress in recent years. The development of new chromophores has enabled highly efficient conversion of low-intensity visible light into UV light. In this review, we summarize the recent development of visible-to-UV TTA-UC, from the development of chromophores and their production into films to their application in various photochemical processes such as catalysis, bond activation and polymerization. Finally, challenges and opportunities in future material development and applications will be discussed.     

Production of a new mucilage compound in Lepidium sativum callus by optimizing in vitro growth conditions

The mucilage in Lepidium sativum L. is considered a biologically active compound with diverse medicinal properties. Different explants (hypocotyls and leaf) were transferred to Murashige and Skoog (MS) medium supplemented with twelve different plant growth regulator combinations under two different incubations (light and dark). The best mucilage production from callus (36.76% g g^?1 dry weight) was obtained in the MS medium supplemented with 1 mg L^?1 of 2, 4-D and 2 mg L^?1 of BAP under the light condition. The mucilage produced by callus culture was nearly three times more than the mucilage yield of the seeds. The glucose, arabinose + mannose and galactose were 43.4 (mg g^?1 DW), 195.3 (mg g^?1 DW) and 86.2 (mg g^?1 DW) in the mucilage originated from seed, callus leaf and callus hypocotyl, respectively. The present study proposes an efficient method for producing large scales of mucilage with a favorable sugar aimed at food or pharmaceutical industries.     

Rapid Isolation of the Trichoderma Strain with Higher Degrading Ability of a Filter Paper and Superior Proliferation Characteristics Using Avicel Plates and the Double-Layer Selection Medium

The cost of cellulase is still a problem for bioethanol production. As the cellulase of Trichoderma reesei is applicable for producing ethanol from cellulosic materials, the cellulase productivity of this fungus should be increased. Therefore, we attempted to develop a system to isolate the strain with higher degrading ability of a filter paper and superior proliferation characteristics among the conidia treated with the mitotic arrester, colchicine. When green mature conidia of T. reesei RUT C-30 were swollen, autopolyploidized, and incubated in the double-layer selection medium containing Avicel, colonies appeared on the surface earlier than the original strain. When such colonies and the original colony were incubated on the Avicel plates, strain B5, one of the colonies derived from the colchicine-treated conidia, showed superior proliferation characteristics. Moreover, when strain B5 and the original strain were compared in the filter paper degrading ability and the cellulose hydrolyzing activity, strain B5 was also superior to the original strain. It was suspected that superior proliferation characteristics of strain B5 reflects higher filter paper degrading ability. Thus, we concluded that the Trichoderma strain with higher degrading ability of a filter paper and superior proliferation characteristics can be isolated using Avicel plates and the double-layer selection medium.     

Control of the Orientation and Photoinduced Phase Transitions of Macrocyclic Azobenzene

Photoinduced phase transitions caused by photochromic reactions bring about a change in the state of matter at constant temperature. Herein, we report the photoinduced phase transitions of crystals of a photoresponsive macrocyclic compound bearing two azobenzene groups ( 1 ) at room temperature on irradiation with UV (365 nm) and visible (436 nm) light. The trans/trans isomer undergoes photoinduced phase transitions (crystal–isotropic phase–crystal) on UV light irradiation. The photochemically generated crystal exhibited reversible phase transitions between the crystal and the mesophase on UV and visible light irradiation. The molecular order of the randomly oriented crystals could be increased by irradiating with linearly polarized visible light, and the value of the order parameter was determined to be ?0.84. Heating enhances the thermal cis‐to‐trans isomerization and subsequent cooling returned crystals of the trans/trans isomer.     

Sorting out the value of spectroscopic tools to assess the Colletotrichum acutatum impact in olive cultivars with different susceptibilities

The olive tree (Olea europaea L.) can be affected by Colletotrichum acutatum, causing a loss of yield and quality of the final products, whilst the incidence of this fungal infection depends on several factors, including cultivar susceptibility. Thus, the effect of C. acutatum infection in cultivars displaying different susceptibilities to this fungal disease (‘Galega Vulgar’ ‐ susceptible, ‘Cobrançosa’ ‐ moderately susceptible, ‘Picual’ ‐ tolerant) has been assessed through spectrophotometric methods and HPLC, while the FTIR spectra of the cuticles have been concomitantly registered, resorting to the ATR accessory. With the support of multivariate analysis, these spectra allowed to discriminate olives with distinct infection times, besides retrieving evidences concerning the different susceptibility of each cultivar, while these observations were reinforced by the spectrophotometric and chromatographic methods. Furthermore, the assessment of the phenolic profile evidenced individual compounds in the distinct cultivars, so as their variations in response to the fungal infection.     

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.     

BLUE and NEAR ULTRAVIOLET REVERSIBLE PHOTOREACTION IN THE INDUCTION OF FUNGAL CONIDIATION

Abstract— The effects of blue light and near UV light on the induction of conidiation in the fungus, Aliernuriu tomato, were investigated. Induction of conidiation was repeatedly controlled by alternating doses of near UV light and blue light. When the final light was near UV, conidiation was induced and conidia developed in the following darkness; when it was blue, the induction of conidiation was suppressed. When conidiation was induced by irradiation with a light mixed with near UV and blue, not only the time lag for inducing conidiation but also the amount of conidia formed were regulated by the fluence rates of both those lights.
Thus, 'mycochrome' is considered to function as a photoreceptor system in the induction of conidiation of this fungus.     

RHYTHMS IN BLUE-LIGHT-INDUCED CONIDIATION OF WILD TYPE AND A MUTANT STRAIN OF Trichoderma harzianum

Abstract— Trichoderma harzianum normally requires light for conidiation. Conidiation of colonies grown in continuous light does not appear to be rhythmic, but sharp banding patterns are formed under light/dark cycles. A single pulse of blue light produces a sharp band of conidia that forms where the growing edge of the mycelia is located at the time when the light is given. A period of about 24 h is required following the light pulse to produce mature conidia. During this time colonies are insensitive to further induction by light. The fluence required to produce 50% saturation varies by a factor of about 3 depending on when the pulse is given. This change of sensitivity is rhythmic with a period length of approximately 27 h when grown on medium containing deoxycholate.
The pattern of conidiation in a mutant strain (B119), which is able to form conidia in the dark, is rhythmic and the period length is dependent on the composition of the medium. Addition of deoxycholate to the medium increased the interval between dark bands from 12 to 24 h. The rhythmic banding is suppressed in constant light and a double banding pattern is produced in light/dark cycles. A pulse of blue light induces a band of conidia in this mutant, as in the wild type, but it also delays the reappearance of the dark banding pattern. The extent of this delay depends on when the pulse is given and, although the period length of the dark conidiation rhythm is affected by deoxycholate, the effect of blue light on its phase is not. Of the various rhythmic responses of Trichoderma studied here. the delay in reappearance of the dark banding pattern in B119 is the most promising for further detailed studies, for example of wavelength and temperature dependence.     

Combining Photodeprotection and Ligation into a Dual-Color Gated Reaction System

We report a photochemical reaction system which requires activation by two colors of light. Specifically, a dual wavelength gated system is established by fusing the visible light mediated deprotection of a dithioacetal with the UV light activated Diels–Alder reaction of an o-methylbenzaldehyde with N -ethylmaleimide. Critically, both light sources are required to achieve the Diels–Alder adduct, irradiation with visible or UV light alone does not lead to the target product. The introduced dual gated photochemical system is particularly interesting for application in light driven 3D printing, where two color wavelength activated photoresists may become reality.     

Mutagenesis and analysis of mold Aspergillus niger for extracellular glucose oxidase production using sugarcane molasses

Aspergillus niger ORS-4.410, a mutant of A. niger ORS-4, was generated by repeated ultraviolet (UV) irradiation. Analysis of the UV treatment dose on wild-type (WT) A. niger ORS-4, conidial survival, and frequency of mutation showed that the maximum frequency of positive mutants (25.5%) was obtained with a 57% conidial survival rate after the second stage of UV irradiation. The level of glucose oxidase (GOX) production from mutant A. niger ORS-4.410 thus obtained was 149% higher than that for WT strain A. niger ORS-4 under liquid culture conditions using hexacyanoferrate (HCF)-treated sugarcane molasses (TM) as a cheaper carbohydrate source. When subcultured monthly for 24 mo, the mutant strain had consistent levels of GOX production (2.62±0.51 U/mL). Mutant A. niger ORS-4.410 was markedly different from the parent strain morphologically and was found to grow abundantly on sugarcane molasses. The mutant strain showed 3.43-fold increases in GOX levels (2.62±0.51 U/mL) using HCF-TM compared with the crude form of cane molasses (0.762±0.158 U/mL). The results reported herein were obtained while the author was working at the Department of Biotechnology, Indian Institute of Technology, Roorkee-247667, India.     

SrTiO_3粉末在可见光照射下光氧化水产氧的研究

SrTiO_3粉末在FeCl_3水溶液里的悬浮体([Fe~(3+)]=1.0×10~(-3)mol/L,pH2.8,SrTiO_3含量1.25g/L)能在λ>400 nm的可见光照射下光氧化水产氧。在相同条件下SrTiO_3和WO_3粉末的混合悬浮体(SrTiO_3与WO_3含量均为1.25g/L)产氧的速率为两者单独存在时的速率之和。光声光谱实验显示SrTiO_3粉末在从溶液里吸附Fe~(3+)后对可见光的吸收大大增强,使它能在可见光下光氧化水产氧。     

Chiral,Thermally Irreversible and Quasi-Stealth Photochromic Dopant to Control Selective Reflection Wavelength of Cholesteric Liquid Crystal

A chiral and thermally irreversible photochromic fulgide derivative incorporating an (R)-binaphthol unit in its acid anhydride moiety was used for the photoswitching of the pitch length of cholesteric liquid crystals. Since the absorption maximum wavelengths of both thermally stable photoisomers are nearly in the UV region (quasi-stealth photochromism), it can be exposed to visible light without inducing photochromic reactions. Therefore, when the photoswitching molecule is added to a permanent cholesteric liquid crystal whose reflection light wavelength is in the visible region, the UV light-induced photochromic reaction of the photoswitching molecule changes the wavelength of the reflection light in the visible light region. We have succeeded in regulating the color of cholesteric liquid crystalline cells between red and blue upon UV light irradiation. Attempts to introduce this system in polymer dispersed cholesteric liquid crystals are also described.     

Visible-light-induced photocatalytic degradation of 4-chlorophenol and phenolic compounds in aqueous suspension of pure titania: demonstrating the existence of a surface-complex-mediated path

The visible-light-induced degradation reaction of 4-chlorophenol (4-CP) was investigated in aqueous suspension of pure TiO2. Contrary to common expectations, 4-CP could be degraded under visible illumination (lambda > 420 nm), generating chlorides and CO2 concomitantly. The observed visible reactivity was not due to the presence of trace UV light since the visible-light-induced reactions exhibited behaviors distinguished from those of UV-induced reactions. Dichloroacetate could not be degraded under visible light, whereas it degraded with a much faster rate than 4-CP under UV irradiation. The addition of tert-butyl alcohol, a common OH radical scavenger, did not affect the visible reactivity of 4-CP, which indicates that OH radicals are not involved. Other phenolic compounds such as phenol and 2,4-dichlorophenol were similarly degraded under visible light. The surface complexation between phenolic compounds and TiO2 appears to be responsible for the visible light reactivity. Diffuse reflectance UV-vis spectra showed that 4-CP adsorbed on TiO2 powder induced visible light absorption. The visible light reactivity among several TiO2 samples was apparently correlated with the surface area of TiO2. The visible-light-induced photocurrents on a TiO2 electrode could be obtained only in the presence of 4-CP. It is proposed that a direct electron transfer from surface-complexed phenol to the conduction band of TiO2 upon absorbing visible light (through ligand-to-metal charge transfer) initiates the oxidative degradation of phenolic compounds. When the surface complex formation was hindered by surface fluorination, surface platinization, and high pH, the visible-light-induced degradation of 4-CP was inhibited. The evidence of visible-light-induced reactions and the experimental conditions affecting the visible reactivity were discussed in detail.