Physicochemical treatments for the reduction of aflatoxins and Aspergillus niger in corn grains (Zea mays)

BACKGROUND

Corn grains are commonly contaminated with mycotoxins and fungi. The purpose of this study was to evaluate the reduction of aflatoxins B₁ , B₂ , G₁ , and G₂ and the inhibition of Aspergillus niger in corn grains using ultrasound, ultraviolet (UV) radiation, electrolyzed water, and sodium bicarbonate. The determination of aflatoxins was performed by high-performance liquid chromatography with fluorescence detection and postcolumn derivatization, and analysis of A. niger was performed by evaluating mycelial growth in potato dextrose agar. The best treatment for reducing aflatoxins and inhibiting mycelial growth was evaluated in corn contaminated with A. niger.

RESULTS

The results show a significant reduction in aflatoxins in the following order: sodium bicarbonate > ultrasound > UV > electrolyzed water for aflatoxins B₁ , B₂ , and G₂ . For aflatoxin G₁ , the order of reduction was sodium bicarbonate > ultrasound > electrolyzed water > UV, with maximum values between 70.50% and 87.03% reached with sodium bicarbonate; for the other treatments, the reduction was between 51.51% and 65.44%. Regarding the fungus, the order of inhibition in the control of mycelial growth was sodium bicarbonate > ultrasound > electrolyzed water > UV in corn grains, and inhibition of mycelial growth was obtained at a sodium bicarbonate concentration of 3.0 g L^-1 .

CONCLUSION

Sodium bicarbonate, electrolyzed water, ultrasound, and UV radiation inhibited the growth of A. niger on potato dextrose agar and reduced the contents of aflatoxins B₁ , B₂ , G₁ , and G₂ in vitro. Sodium bicarbonate showed an ability to inhibit mycelial growth in corn grains. © 2020 Society of Chemical Industry.

Impact of infrared treatment on quality and fungal decontamination of mung bean (Vigna radiata L.) inoculated with Aspergillus spp

BACKGROUND

Mung bean is a rich source of protein, carbohydrates and fiber content. It also exhibits a high level of antioxidant activity due to the presence of phenolic compounds. Aspergillus flavus and A. niger are the two major fungal strains associated with stored mung bean that lead to post-harvest losses of grains and also cause serious health risks to human beings. Thus there is a need to explore an economical decontamination method that can be used without affecting the biochemical parameters of grains.

RESULTS

It was observed that infrared (IR) treatment of mung bean surface up to 70 °C for 5 min at an intensity of 0.299 kW m^-2 led to complete visible inhibition of fungal growth. Scanning electron microscopy revealed that surface irregularities and physical disruption of spores coat are the major reasons behind the inactivation of IR-treated fungal spores. It was also reported that IR treatment up to 70 °C for 5 min does not cause any negative impact on the biochemical and physical properties of mung bean.

CONCLUSION

From the results of the present study, it was concluded that IR treatment at 70 °C for 5 min using an IR source having an intensity of 0.299 kW m^-2 can be successfully used as a method of fungal decontamination. The fungal spore population was reduced (approximately 5.3 log₁₀ CFU g^-1 reductions) without significantly altering the biochemical and physical properties of grains. © 2017 Society of Chemical Industry.

Changes in transcript levels of starch hydrolysis genes and raising citric acid production via carbon ion irradiation mutagenesis of Aspergillus niger

The filamentous ascomycete Aspergillus niger is well known for its ability to accumulate citric acid for the hydrolysis of starchy materials. To improve citric acid productivity, heavy ion beam mutagenesis was utilized to produce mutant A.niger strains with enhanced production of citric acid in this work. It was demonstrated that a mutant HW2 with high concentration of citric acid was isolated after carbon ion irradiation with the energy of 80Mev/μ, which was obvious increase higher than the original strain from liquefied corn starch as a feedstock. More importantly, with the evidence from the expression profiles of key genes and enzyme activity involved in the starch hydrolysis process between original strain and various phenotype mutants, our results confirmed that different transcript levels of key genes involving in starch hydrolysis process between original strain and mutants could be a significant contributor to different citric acid concentration in A.niger, such as, amyR and glaA, which therefore opened a new avenue for constructing genetically engineered A.niger mutants for high-yield citric acid accumulation in the future. As such, this work demonstrated that heavy ion beam mutagenesis presented an efficient alternative strategy to be developed to generate various phenotype microbe species mutants for functional genes research.

[Research of UV-Induced Changes in the Structural and Functional Properties of Inulinases]

UV-induced changes in the catalytic activity and radiuses of inulinases molecules from various producers (plants, fungy, yeast) are studied. It is established that specific enzymes activity and the sizes of inulinases molecules from Helianthus tuberosus and Kluyveromyces marxianus under the influence of UV-light in the ranges of doses 4530-6040 and 755-6040 J/m2, respectively, are subjected to changes more than structural and functional characteristics of inulinase fromAspergillus niger. It is probably connected with lower contents in it of aromatic amino acids such as tyrosine and phenylalanine. The most expressed loss of functional properties of inulinase from Helianthus tuberosus can be caused by the'existence of significantly more numbers of cysteine in plant fructan-exohydrolases in relation to microbic enzymes. A scheme for the stages of response of inulinases of various origins on the influence of UV-light in a certain range of radiation doses is offered.

The impact of dose, irradiance and growth conditions on Aspergillus niger (renamed A. brasiliensis) spores low-pressure (LP) UV inactivation

The use of Aspergillus niger (A. niger) fungal spores as challenge organism for UV reactor validation studies is attractive due to their high UV-resistance and non-pathogenic nature. However A. niger spores UV dose-response was dependent upon sporulation conditions and did not follow the Bunsen-Roscoe Principle of time-dose reciprocity. Exposure to 8 h of natural sunlight for 10 consecutive days increased UV resistance when compared to spores grown solely in dark conditions. Application of 250 mJ cm(-2) at high irradiance (0.11 mW cm(-2)) resulted in a 2-log inactivation; however, at low irradiance (0.022 mW cm(-2)) a 1-log inactivation was achieved. In addition, surface electron microscopy (SEM) images revealed morphological changes between the control and UV exposed spores in contrast to other well accepted UV calibrated test organisms, which show no morphological difference with UV exposure.

Antifungal coatings based on Ca(OH)2 mixed with ZnO/TiO2 nanomaterials for protection of limestone monuments

The presence and deteriorating action of microbial biofilms on historic stone buildings have received considerable attention in the past few years. Among microorganisms, fungi are one of the most damaging groups. In the present work, antimicrobial surfaces were prepared using suspensions of Ca(OH)2 particles, mixed with ZnO or TiO2 nanoparticles. The antimicrobial surfaces were evaluated for their antifungal activity both in the dark and under simulated natural photoperiod cycles, using Penicillium oxalicum and Aspergillus niger as model organisms, and two limestone lithotypes commonly used in construction and as materials for the restoration of historic buildings. Both Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials displayed antifungal activity: ZnO-based systems had the best antifungal properties, being effective both in the dark and under illumination. In contrast, TiO2-based coatings showed antifungal activity only under photoperiod conditions. Controls with coatings consisting of only Ca(OH)2 were readily colonized by both fungi. The antifungal activity was monitored by direct observation with microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and was found to be different for the two lithotypes, suggesting that the mineral grain distribution and porosity played a role in the activity. XRD was used to investigate the formation of biominerals as indicator of the fungal attack of the limestone materials, while SEM illustrated the influence of porosity of both the limestone material and the coatings on the fungal penetration into the limestone. The coated nanosystems based on Ca(OH)2-50%ZnO and pure zincite nanoparticulate films have promising performance on low porosity limestone, showing good antifungal properties against P. oxalicum and A. niger under simulated photoperiod conditions.

[Radiation situation prognosis for deep space: reactions of water and living systems to chronic low-dose ionizing irradiation]

The authors review the findings of researches into the effects of low-dose ionizing irradiation on diverse biological objects (embryonic Japanese quails, Aspergillus niger, Spirostomum ambiguum Ehrbg., mesenchymal stem cells from mouse marrow, dry higher plants seeds, blood lymphocytes from pilots and cosmonauts). Model experiments with chronic exposure to ionizing radiation doses comparable with the measurements inside orbital vehicles and estimations for trips through the interplanetary space resulted in morphological disorders (embryonic Japanese quails, Aspergillus niger), radiation hormesis (Aspergillus niger, MSCs from mouse marrow), increase in the seed germination rate, inhibition of Spirostomum spontaneous activity, DNA damages, chromosomal aberrations, and increase of the blood lymphocytes reactivity to additional radiation loading. These facts give grounds to assume that the crucial factor in the radiation outcomes is changes in liquid medium. In other words, during extended orbiting within the magnetosphere region and interplanetary missions ionizing radiation affects primarily liquids of organism and, secondarily, its morphofunctional structures.

Conjugated polymers for light-activated antifungal activity

A cationic polythiophene-porphyrin (PTP) dyad is shown to exhibit efficient light-activated antifungal activity. Higher singlet oxygen (¹O₂) generation efficiency can be attained from PTP upon photoexcitation due to the light-harvesting properties of the polymer backbone and efficient energy transfer from the polythiophene to the porphyrin units. PTP can be used for treating fungal infections in lower doses of irradiation light and polymer concentration.

Performance of photocatalytic lamps on reduction of culturable airborne microorganism concentration

Reduction of viable airborne Staphylococcus epidermidis and Aspergillus niger spore concentrations using two types of photocatalytic fluorescent lamps under controlled environmental conditions (25 vs. 35°C and 55 vs. 75% relative humidity) were investigated. Visible white-light and UVA black light were in-house spray-coated with TiO(2) and then compared with a commercially coated visible white-light for microbial concentration reduction. The white-light photocatalytic lamps reduced the concentration of culturable S. epidermidis up to 92% independent of temperature or humidity change, while the black light photocatalytic lamps completely inactivated the culturable bacteria at 25°C, 55% relative humidity. Humidity seemed to alleviate UVA damage since better bacteria survival was found. For A. niger spores, rising humidity or temperature could lower their concentration or drop their culturabilities so that a difference between the natural decay and photocatalytic disinfection could not be distinguished. Reductions of total bacteria and total fungi concentrations using these lamps were also examined under uncontrolled environmental conditions in an office and a waste-storage room. It was found that photocatalytic lamps could reduce total culturable bacteria concentration from 9 to 97% and total culturable fungi concentration from 3 to 95% within irradiation time of 30-480 min, respectively. Insignificant difference in concentration reduction among these photocatalytic lamps was pronounced.

Production and characterization of alpha-amylase from Aspergillus niger JGI 24 isolated in Bangalore

Five fungal isolates were screened for the production of alpha-amylase using both solid-state and submerged fermentations. The best amylase producer among them, Aspergillus niger JGI 24, was selected for enzyme production by solid-state fermentation (SSF) on wheat bran. Different carbon and nitrogen supplements were used to enhance enzyme production and maximum amount of enzyme was obtained when SSF was carried out with soluble starch and beef extract (1% each) as supplements. Further attempts to enhance enzyme production by UV induced mutagenesis were carried out. Survival rate decreased with increase in duration of UV exposure. Partial purification of the enzyme using ammonium sulphate fractionation resulted in 1.49 fold increase in the enzyme activity. The enzyme showed a molecular weight of 43 kDa by SDS-PAGE. Metal ions Ca2+ and Co2+ increased the enzyme activity. The enzyme was optimally active at 30 degrees C and pH 9.5.

Strain improvement and up scaling of phytase production by Aspergillus niger NCIM 563 under submerged fermentation conditions

Combination of physical and chemical mutagenesis was used to isolate hyper secretory strains of Aspergillus niger NCIM 563 for phytase production. Phytase activity of mutant N-1 and N-79 was about 17 and 47% higher than the parent strain. In shake flask the productivity of phytase in parent, mutant N-1 and N-79 was 6,181, 7,619 and 9,523 IU/L per day, respectively. Up scaling of the fermentation from shake flask to 3 and 14 L New Brunswick fermenter was studied. After optimizing various fermentation parameters like aeration, agitation and carbon source in fermentation medium the fermentation time to achieve highest phytase activity was reduced considerably from 14 days in shake flask to 8 days in 14 L fermenter. Highest phytase activity of 80 IU/ml was obtained in 1% rice bran-3.5% glucose containing medium with aeration 0.2 vvm and agitation 550 rpm at room temperature on 8th day of fermentation. Addition of either bavistin (0.1%), penicillin (0.1%), formalin (0.2%) and sodium chloride (10%) in fermented broth were effective in retaining 100% phytase activity for 8 days at room temperature while these reagents along with methanol (50%) and ethanol (50%) confer 100% stability of phytase activity at 4 degrees C till 20 days. Among various carriers used for application of phytase in feed, wheat bran and rice bran were superior to silica and calcium carbonate. Thermo stabilization studies indicate 100% protection of phytase activity in presence of 12% skim milk at 70 degrees C, which will be useful for its spray drying.

Adaptive melanin response of the soil fungus Aspergillus niger to UV radiation stress at "Evolution Canyon", Mount Carmel, Israel

Background

Adaptation is an evolutionary process in which traits in a population are tailored by natural selection to better meet the challenges presented by the local environment. The major discussion relating to natural selection concerns the portraying of the cause and effect relationship between a presumably adaptive trait and selection agents generating it. Therefore, it is necessary to identify trait(s) that evolve in direct response to selection, enhancing the organism's fitness. “Evolution Canyon” (EC) in Israel mirrors a microcosmic evolutionary system across life and is ideal to study natural selection and local adaptation under sharply, microclimatically divergent environments. The south-facing, tropical, sunny and xeric “African” slope (AS) receives 200%–800% higher solar radiation than the north-facing, temperate, shady and mesic “European” slope (ES), 200 meters apart. Thus, solar ultraviolet radiation (UVR) is a major selection agent in EC influencing the organism-environment interaction. Melanin is a trait postulated to have evolved for UV-screening in microorganisms. Here we investigate the cause and effect relationship between differential UVR on the opposing slopes of EC and the conidial melanin concentration of the filamentous soil fungus Aspergillus niger. We test the working hypothesis that the AS strains exhibit higher melanin content than strains from the ES resulting in higher UV resistance.

Methodology/Principal Findings

We measured conidial melanin concentration of 80 strains from the EC using a spectrophotometer. The results indicated that mean conidial melanin concentration of AS strains were threefold higher than ES strains and the former resisted UVA irradiation better than the latter. Comparisons of melanin in the conidia of A. niger strains from sunny and shady microniches on the predominantly sunny AS and predominantly shady ES indicated that shady conditions on the AS have no influence on the selection on melanin; in contrast, the sunny strains from the ES displayed higher melanin concentrations.

Conclusions/Significance

We conclude that melanin in A. niger is an adaptive trait against UVR generated by natural selection.

Citric acid production by a novel Aspergillus niger isolate: I. Mutagenesis and cost reduction studies

Ultraviolet-irradiation (UV), ethyl methane sulfonate (EMS) and acridine orange (AO) were used to induce citric acid overproduction mutations in Aspergillus niger UMIP 2564. Among 15, eight of the mutant derivatives, were improved with respect to citric acid production from sucrose in batch cultures. Maximum product yield (60.25%) was recorded by W5, a stable UV mutant, with approximately 3.2-fold increase when compared to the parental wild type strain. In terms of the kinetic parameters for batch fermentation processes, the mutation doubled the specific substrate uptake rate and achieved 4.5- and 7.5-fold improvements in citric acid productivity and specific productivity, respectively. For reduction of the fermentation medium cost, corn steep liquor and calcium phosphate pre-treated beet molasses were successfully used as substituents of nitrogen and carbon sources in the growth medium, respectively. These medium substitutions resulted in a W5 citric acid fermentation culture with a product yield of 74.56%.

Highly efficient gene targeting in the Aspergillus niger kusA mutant

Gene targeting frequencies in Aspergillus niger are often very low and hamper efficient functional genomics in this biotechnologically important fungus. Deletion of the A. niger kusA gene encoding the ortholog of the Ku70 protein in other eukaryotes, dramatically improved homologous integration efficiency and reached more than 80% compared to 7% in the wild-type background, when 500bp homologous flanks were used. Furthermore, the use of the DeltakusA strain resulted in a high frequency of heterokaryon formation (70%) in primary transformants in the case disrupting an essential gene. Deletion of kusA had no obvious effect on the growth of the fungus, but renders the DeltakusA strain 10 times more sensitive to X-ray irradiation and two to three times more sensitive to UV exposure. The highly efficient gene targeting in combination with the A. niger genome sequence allows a systematic approach to generate gene knockouts and will help in improving the capacities of A. niger as producer of commercially interesting proteins and metabolites.

[Study on the asexual sporulation of Aspergillus niger under blue light induction and analysis of its subtractive library]

The effect of blue light (BL) on the morphological development of Aspergillus niger was studied by the scanning electron microscopy (SEM) observation. Comparing with the darkness, BL was able to stimulate development of sporangiophore and conidiosphore, promote grownth of mycelium. Suppression subtractive hybridization (SSH) was conducted with tester cDNA which was from 39 to approximately 40h-old mycelium cultured under darkness and driver cDNA which was from mycelium illuminated for 3 to approximately 4h under BL after dark growth. Some cDNA bands were obtained by suppression PCR (polymerase chain reaction) with the subtractive cDNA. Positive bacterial clones were randomly picked and identified by colony PCR method. Through sequence alignments from GenBank, most of differential cDNA fragments were highly identical with some redox enzymes existing in mitochondria, and the quantitative measurement of these differential mRNA by real time RT-PCR indicated that relative expression of the identified gene fragments under BL induction was higher than that under darkness. Furthermore, the result suggested that some respiratory chain redox enzymes of mitochondria were involved in the photoresponse and consequently influence the metabolism. Among differential cDNA fragments two unkown sequences were found and their complete gene and gene function remained to be investigated.

[Effect of blue light on conidiation development and glucoamylase enhancement in Aspergillus niger]

Pure blue (BL) or red light (RL) were obtained by filtering blue or red fluorescent lamp light through plastic filters. With the dark condition as control, the effect of BL and RL on the Aspergillus niger were studied including soluble protein content of mycelium, glucoamylase activity, the biomass as well as sporangiophore photomorphogenesis and vegetative spore development. Irradiation with BL and RL wholly promoted glucoamylase activity together with the rise of the soluble protein content and the mycelium growth. The glucoamylase activity of mycelia culture under blue light was enhanced 2.54 times than that of control. In the phases of developmental growth (young mycelia and sporangiophores), glucoamylase activity and relative conductivity ratio of mycelium were higher under blue light than under dark, the enhanced glucoamylase activity likely stemmed from development of macrosporangiophores of Aspergillus niger promoted by blue light. In addition, the increase of glucoamylase activity under blue light was highest at the stage of macrosporangiophores forming and conidiation, then declined owing to spores aging. As to young microsporangiophores under darkness the glucoamylase activity just relatively increased and declined rapidly with age. Different from control, irradiation with blue light at the time of 72 h after inoculation was able to stimulate development of macrosporangiophore and conidium along with the rise of glucoamylase activity of Aspergillus niger.

Resistance of stratospheric and mesospheric micro-organisms to extreme factors

Studies of the stratosphere and mesosphere, by means of special analysers installed on meteorological rockets, have thrown more light on our knowledge of the upper boundary of the biosphere. The presence of the following micro-organisms was registered at heights of 49-77 km: Aspergillus niger, Penicillium notatum, Circinella muscae, Papulaspora anomala, Mycobacterium luteum and Micrococcus albus. The isolated micro-organisms were subjected to the action of gamma-irradiation, high vacuum and UV radiation in order to evaluate the quality of sterilization by gamma-rays (3.2-3.5 Mrad) prior to sampling and the resistance of these micro-organisms to physical factors of the stratosphere and mesosphere. No species with high radio-resistance were detected among the isolated cultures. The D10 index for fungal spores and bacterial vegetative cells, freeze-dried or suspended in a physiological solution, did not exceed 290 krad. These data confirm that sterilization of the analyser with gamma-rays assured the purity of biological experiments during sampling. The isolated micro-organisms were found to be very resistant to high vacuum (10(-9) mmHg) and UV radiation, with the exception of the pigmentless Micrococcus albus. This evidence shows that pigmented micro-organisms can survive in the earth's atmosphere at high altitudes.

Effect of volume of culture medium on enhanced citric acid productivity by a mutant culture of Aspergillus niger in stirred fermentor

AIMS

The present study deals with the effect of volume of culture medium on enhanced citric acid productivity by a mutant culture of Aspergillus niger.

METHODS AND RESULTS

A laboratory scale stirred fermentor of 15-l capacity was employed for all microbial cultivations. Blackstrap molasses, a by-product of sugar industries is easily and abundantly available for its exploitation as a carbon source in fermentation processes. The parental culture of A. niger was improved by mutation using ultraviolet radiations and N-methyl N-nitro N-nitroso guanidine, i.e. mutagen MNNG. Six MUV and eight MNNG-treated mutant strains were isolated after extensive screening and optimization. Mutant strain of A. niger MNNG-2 showed enhanced citric productivity (87.60 g l-1) over the parental strain BTL-45 (19.53 g l-1) and other mutant derivatives (49.85 g l-1 citric acid in case of mutant MUV-5 and 76.82 g l-1 in case of mutant MNNG-7). The optimal sugar level was found to be 150 g l-1 (optimum volume of the medium, 60%) after 6 days of inoculation, which is economically significant. Specific productivity of the mutant culture MNNG-2 (qp = 0.057 g/g cells h-1) was several folds higher than other strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of the present study are of commercial level. All kinetic parameters including yield coefficients and volumetric rates revealed the hyper-producibility of citric acid by mutant MNNG-2 using blackstrap molasses as the basal medium in stirred fermentor.

The "SCORPION" experiment onboard the International Space Station. Preliminary results

The "SCORPION" program onboard the Russian Segment (RS) of the International Space Station (ISS) is designed to carry out complex research of the effects of the nar-Earth space parameters on the conditions under which various experiments and operations are being conducted. Special attention in this program was paid to the biological objects onboard the orbital station, e.g. it was found that variation in the number of colony forming units (micromicets and bacteria) correlates with the solar activity and the absorbed dose. The "SCORPION" experiment onboard the RS ISS started in January 2002. It was designed to measure the following parameters inside the space absorbed doses in different places inside the RS ISS, the fluxes of energetic charged particles, neutrons and gamma-quanta; the vectors of the magnetic field and low-frequency electromagnetic waves. At the same time the growth of micromicets on the samples of various materials was studied. The description of the "SCORPION" experiment and the preliminary results obtained onboard the RS ISS in 2002 are presented.

Exposure of microorganisms to simulated extraterrestrial space ecology

Spores of five test organisms, Bacillus subtilis var. niger, Bacillus megaterium, Bacillus stearothermophilus, Clostridium sporogenes and Aspergillus niger and soils were exposed, while under ultra high vacuum to temperatures of from -190 degrees C to +170 degrees C for 45 days. Up to a temperature of 25 degrees C no loss in viability of the test spores were noted when compared to original populations maintained at room temperature at atmospheric pressure over a desiccant. At elevated temperatures differences in resistivity occurred so that at 88 degrees C only B. subtilis var. niger and A. niger survived in appreciable numbers. At 107 degrees C only A. niger spores survived, but none were recoverable after exposure to 120 degrees C. In comparison B. subtilis var. niger survived at atmospheric pressure and 90 degrees C for 5 days while none of the other spores were viable after 48 hours. Four groups of organisms in soil, mesophilic aerobes and anaerobes, molds and actinomycetes were similarly tested in the vacuum chamber. From one soil sample only actinomycetes survived 120 degrees C, whereas one other soil sample yielded viable bacteria after exposure to 170 degrees C. The resistance of the isolates to high temperatures in the absence of soil is being evaluated. Several organisms have been found to resists 120 degrees C in ultra-high vacuum for 4-5 days, and experiments at higher temperatures are in progress. When irradiated with gamma rays from a cobalt-60 source, there was a difference between vacuum dried test spores irradiated while still under vacuum to those exposed to air immediately before irradiation. A reduction of from one-third to one-ninth of the viability of spores irradiated in vacuum occurred with vacuum-treated spores irradiated in air.

Survival of microorganisms under the extreme conditions of the Atacama Desert

Spores of Bacillus subtilis, conidia of Aspergillus niger, versicolor and ochraceus and cells of Deinococcus radiodurans have been exposed in the dark at two locations (at about 23 degrees S and 24 degrees S) in the Atacama Desert for up to 15 months. B. subtilis spores (survival approximately 15%) and A. niger conidia (survival approximately 30%) outlived the other species. The survival of the conidia and spores species was only slightly poorer than that of the corresponding laboratory controls. However, the Deinococcus radiodurans cells did not survive the desert exposure, because they are readily inactivated at relative humidities between 40 and 80% which typically occur during desert nights. Cellular monolayers of the dry spores and conidia have in addition been exposed to the full sun light for up to several hours. The solar fluences causing 63% loss in viability (F37-values) have been determined. These F37-values are compared with those determined at other global locations such as Punta Arenas (53 degrees S), Key Largo (25 degrees N) or Mainz (50 degrees N) during the same season. The solar UVB radiation kills even the most resistant microorganisms within a few hours due to DNA damages. The data are also discussed with respect to possible similarities between the climatic conditions of the recent Atacama Desert and the deserts of early Mars.

Effect of gamma irradiation on storability of apples (Malus domestica L.)

The aim of this study was to investigate the effect of gamma irradiation on storability of the two main apple varieties, Golden Delicious and Starking, in Syria. The experiments were performed in 1995 and 1996. Fruits were irradiated with 0, 0.5, 1.0 and 1.5 KGy. Irradiated and unirradiated fruits were stored at 1 to 2 degrees C and under a relative humidity of 80 to 90%. Weight loss and spoilage due to physiological disorders and fungal diseases were evaluated throughout the different storage periods. Firmness, coloration and pH values were estimated immediately after irradiation. The results showed that, in both varieties, gamma irradiation increased the weight loss after 45 days of storage in apples gathered in 1995 but not in the 1996 season. After 180 days of storage, gamma irradiation had different effects on weight loss depending on the growing year and variety, and increased fungal spoilage. Application of gamma irradiation prevented the growth of Aspergillus niger and the formation of skin scald in 'Golden Delicious' fruits. Immediately after treatment, gamma irradiation increased the softening of fruits, changed their color from green to yellow and decreased the pH value of the juice.

Cobalt 60 radiation and growth of eleven species of micro-fungi from Evolution Canyon, Lower Nahal Oren, Israel

Eleven micro-fungal species isolated from both the north facing slope (NFS) and the south facing slope (SFS) of Evolution Canyon, Lower Nahal Oren, Israel, were examined for growth rates before and after exposure to 60Co irradiation. Species of Alternaria, Aspergillus, Humicola, Oidiodendron, and Staphylotrichum from SFS grew faster than the NFS isolates while Fusarium, Sordaria, and Stachybotrys grew at greater rates from the NFS than from the SFS. Mucor and Ulocladium isolates grew at the same rate from both SFS and NFS. The eleven isolates from each slope were next subjected to 60Co irradiation. At 40,000 rads exposure, Alternaria, Fusarium, and Stachybotrys grew more rapidly when isolated from the NFS, while Humicola and Staphylotrichum grew at a faster rate when isolated from the SFS. Aspergillus, Mucor, Sordaria, and Ulocladium from both the NFS and the SFS had relatively the same growth rate at 40,000 rads exposure. At 400,000 rads exposure, growth rates remained much the same for both the N and S exposed isolates as they were at 40,000 rads. Above 10(6) rads, growth ceased but recovery occurred at various times for individual isolates of the same species from opposing canyon slopes.

Effect of gamma irradiation on the production of cell wall degrading enzymes by Aspergillus niger

Fungi occurring in Egyptian fruits in the City of Qena were studied. Results from the examination of 25 replicated samples of plums, pears and apples are reported. Examinations were carried out by direct plating after surface disinfection in a 0.5% (w/v) calcium hypochlorite solution on Czapek's-Dox agar. The dominant fungus found in the three types of fruit was Aspergillus niger, which was present in 88% of plum samples, 80% of pear samples and all of the apple samples. The lowest dose of gamma irradiation (1 MCi for 10 min) enhanced the three isolates of A. niger investigated to produce more biomass and polygalactronase, pectinmethylglacturonase, cellulase and protease. The higher doses (1 MCi for 20 and 30 min) were inhibitory to the growth of A. niger.

Enhancement of inulinase production by Aspergillus niger van Teighem

Aspergillus niger van Teighem, a soil isolate, was mutagenized by u.v. light. A mutant strain with 3 times increased productivity was generated on exposure of the parent strain to u.v. for 15 min. This mutant on further exposure to u.v. yielded second generation mutants with only marginal increase in inulinase productivity with respect to the parent mutant, but the best yield of 377 U ml-1 was considered promising for industrial use.

Disinfection efficacy in an integrated ultraviolet light contact lens care system

We evaluated a new integrated contact lens care system that combines fluid turbulence for lens cleaning with ultraviolet (UV) light for solution sterilization. The ultraviolet light system was used to clean and disinfect 42 soft contact lenses (water contents: 38.6%, 43%, 55%, and 70%) and two rigid gas permeable lenses. Test lenses were contaminated with 10(6) cells/mL of Bacillus pumilus, Aspergillus niger, Pseudomonas aeruginosa, and Acanthamoeba castellanii and subjected to a 15-minute cleaning-disinfection cycle. Bathing solutions and contact lenses were cultured at various time intervals and at the end of the cycle. All bathing solutions and all lenses but one were found to be sterile after one cycle. All units effectively disinfected solutions and contact lenses. This device may be an effective alternative to existing contact lens care systems.

Enhancement of beta-galactosidase productivity of Aspergillus niger NCIM-616

A series of mutations was carried out with Aspergillus niger NCIM-616 as the parent strain. A mutant strain NG-4 with 28% increased beta-galactosidase productivity was produced with N-methyl-N-nitro-N-nitrosoguanidine (NTG) at 1500 micrograms ml-1 concentration and exposure time of 60 min. This mutant yielded a third generation u.v.-treated strain, UV-5 with a 117.6% increase in beta-galactosidase productivity with respect to the parent strain.

Ultraviolet radiation for the sterilization of contact lenses

Two sources of ultraviolet (UV) radiation with peak wavelengths in the UV-C or UV-B ranges were compared for their ability to sterilize contact lenses infected with Pseudomonas aeruginosa, Streptococcus pneumoniae, Acanthamoeba castellani, Candida albicans, and Aspergillus niger. Also examined was the effect of prolonged UV light exposure on soft and rigid gas permeable (RGP) contact lenses. The UV-C lamp (253.7 nm, 250 mW/cm2 at 1 cm) was germicidal for all organisms within 20 minutes but caused destruction of the soft lens polymers within 6 hours of cumulative exposure. UV-C caused damage to RGP lenses in less than 100 hours. The UV-B lamp (290-310 nm, 500 mW/cm2 at 1 cm) was germicidal for all organisms tested (except Aspergillus) with a 180-minute exposure and caused less severe changes in the soft lens polymers than did the UV-C lamp, although cumulative exposure of 300 hours did substantially weaken the soft lens material. RGP materials were minimally affected by exposure to 300 hours of UV-B. Ultraviolet light is an effective germicidal agent but is injurious to soft lens polymers; its possible utility in the sterilization of RGP lenses and lens cases deserves further study.

Sterilization efficacy of ultraviolet irradiation on microbial aerosols under dynamic airflow by experimental air conditioning systems

In order to know the sterilization efficacy of ultraviolet irradiation on microbial aerosols, the size and the weight of the aerosol particles were evaluated, and these were irradiated under dynamic air flow created by an experimental air conditioning system. The experimental apparatus consisted of a high efficiency particulate air (HEPA) filter, an aerosol generator, spiral UV lamps placed around a quart glass tube, an Andersen air sampler and a vacuum pump. They were connected serially by stainless steel ducts (85 mm in diameter, 8m in length). Six types of microbial aerosols generated from an ultrasonic nebulizer were irradiated by UV rays (wavelength 254nm, mean density 9400 microW/cm2). Their irradiation time ranged from 1.0 to 0.0625 seconds. The microbial aerosols were collected onto the trypticase soy agar (TSA) medium in the Andersen air sampler. After incubation, the number of colony forming units (CFU) were counted, and converted to particle counts. The diameter of microbial aerosol particles calculated by their log normal distribution were found to match the diameter of a single bacteria cell measured by a microscope. The sterilization efficacy of UV in standard airflow conditions (0.5 sec. irradiation) were found to be over 99.5% in Staphylococcus aureus, Staphylococcus epidermidis, Serratia marcescens, Bacillus subtilis (vegetative cell) and Bacillus subtilis (spore) and 67% in Aspergillus niger (conidium). In A. niger, which was the most resistant microbe to UV irradiation, the efficacy rose up to 79% when irradiated for 1.0 sec., and it was observed that the growth speed of the colonies was slower than that of the controls. It was thought that UV rays caused some damage to the proliferation of A. niger cells.

[Comparative physiological and biochemical characteristics of Aspergillus niger isolated from the mesosphere and of its mutant]

The aim of this work was to study certain physiological-biochemical characteristics of Aspergillus niger, strain 26, isolated from the mesosphere as well as those of its mutant having light-brown conidia. The parent strain and its mutant were grown in a liquid Chapek medium to study accumulation of the biomass, changes in the pH of the medium, as well as assimilation of glucose, nitrogen (NO3-) and phosphorus (PO4-). The content of polysaccharides, protein, RNA and DNA was determined in the biomass. The parent culture and its mutant had the same growth dynamics and changes in the pH of the growth medium. They assimilated nitrogen, phosphorus and glucose at the same rate. No significant differences were found in the content of DNA, RNA, protein and polysaccharides. Lipids were an exception: their content was higher by ca. 26% in the mutant as compared with the parent strain. Apparently, the elevated sensitivity of the mutant to UV is due not only to a loss of certain pigments, but also to a damage of other protective mechanisms of the cell.

[Resistance of microorganisms of upper layers of the atmosphere to ultraviolet radiation and a high vacuum]

Solar radiation and high vacuum are the main factors affecting the incidence of microorganisms in the stratosphere and mesophere. It has been established in experiments that the conidia of Aspergillus niger are most resistant of UV irradiation. The conidia of Penicillium, the spores of Papulaspora anomala and Circinella muscae, and the vegetative cells of Micrococcus and Mycobacterium are more susceptible to UV radiation. All of the isolated microorganisms have been shown to be resistant to high vacuum. Their inactivation varied within the range of 2 to 16%, with an exception of Micrococcus cells (40%).

[Change in ratio between citric and oxalic acid in Aspergillus niger upon exposure to mutagenic factors]

Stepwise selection of Aspergillus niger producing citric acid in highly buffered molassa media was carried on in order to decrease the biosynthesis of oxalic and gluconic acids using the following mutagenic factors: diethyl sulfate, thiophosphamide, cyclophosphan, N-methyl-N'-nitro-N-nitrosoguanidine (NG), 5-fluorouracil, 1,4-bis-diazoacetylbutane, and UV. The ratio between the acids changed in mutants obtained upon the combined treatment with UV and NG. Mutants producing twice as less oxalic acid were characterized by weak growth and formation of conidia.

MICROORGANISMS OF THE UPPER LAYER OF THE ATMOSPHERE AND THE PROTECTIVE ROLE OF THEIR CELL PIGMENTS

Of the six species of microorganisms isolated from the mesosphere, five contained pigments and were more resistant to UV radiation compared with their pigment-free mutants. The black pigment isolated from the conidia of Aspergillus niger considerably increased the UV resistance of the unpigmented mutant conidia of Penicillium notatum, the spore Circinella muscae and the vegetative cells of Micrococcus albus. From the data it is possible to conclude that in the upper layers of the Earth's atmosphere the predominant proportion of pigmented microorganisms is the consequence of natural selection by UV radiation.

Spontaneous segregation of a heterozygous diploid of Aspergillus niger

A case of spontaneous segregation of a heterozygous diploid was observed with Aspergillus niger, giving rise to a somatic recombinant. Assuming an independence of markers, its genotype is suggested to be brw+lys pab+brw lys+pab.

Improved production of citric acid by a diploid strain of Aspergillus niger

Aspergillus niger strain CGU 87 was treated with UV radiation and some auxotrophic mutants were obtained. These mutants were less productive than CGU 87, which produced an average of 7.4% citric acid. All possible crosses in pair wise combinations were carried out between these auxotrophs, and three heterokaryons were synthesised. Finally, one heterozygous diploid was isolated from each of them. These heterokaryons and diploids showed improved productivity when compared with their component parents, but except in one diploid D5, all others produced less citric acid than CGU 87. The yield of D5 exceeded that of CGU 87 by 1.2 times and it produced 9% citric acid. This is a significant improvement and the increased productivity seems to be the result of successful adaptation of D5 to its fermentation environment.

Light stimulated 'shunt-metabolism' succinate-alpha-ketoglutarate-isocitrate cycle and accumulation of citric acid in Aspergillus niger

Studies with light of the visible range had shown that light plays significant role in the biosynthesis and accumulation of citric acid in Aspergillus niger. Accumulation of 14C-labelled carbon atoms in alpha-ketoglutaric, isocitric, succinic and glycolic acids in the cultures grown under illumination suggest a probable 'shunt-metabolism' leading to the succinate-alpha-ketoglutarate-isocitrate (SKI) cycle. This shunt metabolism minimizes the accumulation of citric acid in cultures due to depletion of intermediates.