不同地理和寄主来源的串珠镰孢的营养体亲和性研究

选用107个采自安徽、山东、江苏、湖北等不同地区棉花、玉米、水稻的串珠镰孢Fusarium moniliforme菌株,在含KClO3培养基上诱导筛选获得抗氯酸盐、不能还原利用硝酸盐的突变株(nitmutant)1081株,在MM、NM、HM等3种不同氮源培养基上划分出nitA、nitB、nitC、nitD四种突变类型,其中nitA出现频率最高,占总体76%;nitB和nitC其次,分别占12%和10%;nitD最少,占总体2%。采用nit突变体互补型配对技术,将供试菌株分别按地理来源和分离寄主进行配对培养,测得不同寄主群体内菌株的营养体亲合群(VCGs)数为56个,然后从每个VCG中随机抽取1个样本菌株,测定不同群体间菌株的VCG同一性,发现所抽取的56个菌株分属于54个VCGs,其中来自棉花的菌株Fm1、Fm2分别与来自玉米的菌株Fm19、Fm20属于同一VCG。按地理来源测定,4个群体共测得55个VCGs,其中来自山东的菌株Fm45和来自安徽的菌株Fm16发生亲和反应,属于同一VCG;107个菌株划分为54个VCGs。结果表明,串珠镰孢菌株群体内存在丰富的VCGs多样性。经多样性分析,不同地理来源的菌株平均1.9454个组成1个VCG,其P与Shannon-Wiener多样性指数分别为0.5140和1.0365;不同寄主上分离的菌株平均1.9107个形成1个VCG,P与Shannon-Wiener多样性指数分别为0.5234和0.9048。经t测验,两个群体Shannon-Wiener多样性指数H值间差异不显著(t=0.70小于t0.05=1.98),说明两个群体的VCG多样性无显著差异,相同地区来源的菌株的遗传相似性与相同寄主来源的遗传相似性相当。     

Occurrence and toxigenicity of shape Fusarium moniliforme from freshly harvested maize ears with special references to fumonisin production in Egypt

Using the seed-plate technique, 18 different isolates of Fusarium moniliforme were isolated on pentachloronitrobenzene (PCNB) agar medium from 18 samples of a local variety of corn collected from locations in Minia Governorate. The isolates of F moniliforme were screened for their ability to produce fumonisins on polished rice grains using the solid state fermentation technique. Based on thin layer chromatographic (TLC) analyses using silica gel plates, 14 of the 18 isolates tested produced FB₁ and FB₂ with R _f (0.17) and (0.24), respectively. Concentration of FB₁ was estimated using high performance liquid chromatography (HPLC). Production of FB₁ by the 14 isolates of F. moniliforme tested ranged from 69 to 4495 ppm indicating that mouldy corn may represent a health hazard to consumers. This revised version was published online in August 2006 with corrections to the Cover Date.     

A medium for inducing conversion of Histoplasma capsulatum var. capsulatum into its yeast-like form.

Histoplasma capsulatum var. capsulatum is a dimorphic fungus that, under special conditions, converts from its more common mycelial form to a yeast-like form. Achieving this conversion, however, has been problematical for researchers. The present study tested conversion rates in ten Histoplasma capsulatum var. capsulatum strains using seven culture media, four of which were conventional and three novel. One of our novel media, MLGema, induced complete conversion of two strains within five days of incubation at 35 degrees C, and of all strains that eventually converted by the time of the second subculturing transfer, under defined experimental conditions. MLGema is also inexpensive and easy to produce.     

Secretion of β-galactosidases by Aureobasidium pullulans and Penicillium brevicompactum on polygalacturonate medium

An assay has been developed to detect production of extracellular β -galactosidases by fungi during growth on a defined medium containing polygalacturonate. Using this method strains of the yeast-like fungus Aureobasidium pullulans and the filamentous fungus Penicillium brevicompactum which secrete β -galactosidase have been isolated. Seventy strains of yeast were tested but none secrete detectable extracellular β -galactosidase during growth on polygalacturonate agar medium.     

Ultrastructure and cell wall chemistry of a thermosensitive mutant ofParacoccidioides brasiliensis

Results of chemical analysis and ultrastructural study of the cell wall of a thermosensitive dimorphic mutant ofParacoccidioides brasiliensis support the involvement of α-1,3-glucan in the process of dimorphism, but do not support a possible role of this glucan as being responsible for the yeast-like morphology of this pathogenic fungus.     

One-step transformation of the dimorphic yeast Yarrowia lipolytica

An efficient one-step transformation method for the dimorphic yeast Yarrowia lipolytica is described. Using cells grown overnight on agar plates, the whole process is carried out within 1 h. The transformant clones could be recovered on selective plates as early as 36–48 h after plating. The efficiency was better than 10⁵ transformants/μg replicative plasmid DNA. Effects of cell density, dithiothreitol, heat shock, poly(ethylene glycol) 4000 concentration and the wetness of selective plates were investigated. Received: 17 February 1997 / Received revision: 4 April 1997 / Accepted: 19 April 1997     

<Emphasis Type="Italic">Fusarium verticillioides</Emphasis>: Evaluation of Fumonisin Production and Effect of Fungicides on In Vitro Inhibition of Mycelial Growth

The objectives of this study were to evaluate the fumonisin production by 16 F. verticillioides strains on corn cultures and the effect of quintozene and fludioxonil + metalaxyl-M fungicides on “in vitro” mycelial growth on agar. In addition, the effect of fludioxonil + metalaxyl-M on fumonisin production in defined liquid culture medium was analyzed. Fumonisin B₁ levels on corn cultures ranged from 2.41 to 3996.36 μg/g and the F. verticillioides 103F strain produced the highest level (3996.36 ± 390.49 μg/g, P < 0.05). F. verticillioides strains were inoculated in potato dextrose agar with the addition of quintozene (75 to 9,375 μg/ml) and fludioxonil + metalaxyl-M (1.5 + 0.6 to 187.5 + 75 μg/ml) in order to evaluate the effect of these fungicides on “in vitro” mycelial growth. The F. verticillioides strains showed great variability concerning ED₅₀ values, which were below the recommended application dose for quintozene, but above that for fludioxonil + metalaxyl-M. Moreover, fungicide addition to the culture medium increased mean FB₁ levels compared to the control, suggesting the importance of focusing on the effect of fungicides on mycotoxin production as well as on the phytopathogen control.     

Screening of microorganisms for biodegradation of poly(lactic-acid) and lactic acid-containing polymers.

The ability of some microorganisms to use lactic acid stereocopolymers and copolymers with glycolic acid as sole carbon and energy sources was studied under controlled or natural conditions. First, 14 filamentous fungal strains were tested in liquid cultures, adopting total lactic acid consumption, nitrogen source exhaustion, and maximal biomass production as selection criteria. Two strains of Fusarium moniliforme and one strain of Penicillium roqueforti were able to totally assimilate DL-lactic acid, partially soluble racemic oligomers (MW = 1,000), and the nitrogen source. Only one strain of F. moniliforme was able to grow on a poly(lactic acid)-glycolic acid copolymer (MW = 150,000) after 2 months of incubation at 28 degrees C on synthetic agar medium. Mycelium development was examined by scanning electron microscopy. F. moniliforme filaments were observed to grow not only at the copolymer surface but also through the bulk of the copolymer. In a second approach, plates made of a racemic poly(lactic acid) were buried in the soil before being incubated in petri dishes containing mineral agar medium under controlled conditions. Five strains of different filamentous fungi were isolated, and their ability to assimilate racemic poly(lactic acid) oligomers was tested in liquid cultures.     

Disruption of two genes for chitin synthase in the phytopathogenic fungus Ustilago maydis

The phytopathogenic fungus Ustilago maydis exhibits a dimorphic transition in which non-pathogenic, yeast-like cells mate to form a pathogenic, filamentous dikaryon. Northern analysis indicated that two chitin synthase genes, chs1 and chs2, from U. maydis are expressed at similar levels in yeast-like cells and in cells undergoing the mating reaction leading to the filamentous cell type. A mutation was constructed in each of the chitin synthase genes by targeted gene disruption. Each mutant showed a reduction in the level of trypsin-activated enzyme activity, compared with a wild-type strain, but retained the wild-type morphology, the ability to mate and the ability to form the filamentous pathogenic cell type.     

7种甲真菌病致病菌的侵袭力比较

目的观察红色毛癣菌、白念珠菌、红酵母、短帚霉、串珠镰刀菌、烟曲霉、绳状青霉是否具有侵犯离体甲板的能力,并比较其侵袭能力的强弱。方法将无菌甲板接种于红色毛癣菌、白念珠菌、红酵母、短帚霉、串珠镰刀菌、烟曲霉、绳状青霉7种真菌的3种不同培养基(固体沙氏培养皿、液体沙氏试管及生理盐水试管)中,定期用NaOH溶甲法分析甲板受侵程度。结果某些非皮肤癣菌性丝状真菌侵犯体外甲板的能力与红色毛癣菌基本相同,但丝状真菌比酵母菌强,酵母菌中白念珠菌比红酵母强。同一种真菌在固体培养基上对甲板的侵袭力远比在液体培养基中或生理盐水中强。结论一定条件下,某些非皮肤癣菌也能直接侵犯甲板。真菌侵犯甲的能力与其形成菌丝的能力及其与甲板接触的稳定性成正比。     

Simple rapid identification of Candida albicans with emphasis on the differentiation between Candida albicans and Candida stellatoidea

Summary Subcultures ofC. albicans, made from Sabouraud agar, grown at room temperature for 48 hours, were inoculated into a 10 times saline dilution of Sabouraud liquid medium and left in the incubator for 45–60 minutes at 37° C, transferred to corn meal agar plates and incubated at 37° C for 18–24 hours.Small portions of the surface agar containing the yeasts from these plates were pressed under cover glasses and examined under the oil immersion lens.Under these conditions,C. albicans cultures were observed to produce only yeast-like cells, whereasC. stellatoidea cultures contained predominantly abundant, long, thin mycelia.     

Fungicidal and binding properties of three plant peptides

The fungicidal properties of plant seed peptides from Heuchera sanginea (Hs-AFP₁), Raphanus sativus (EA-AFP₂), and Impatiens balsamina (Ib-AMP₃) were determined for the nongerminated and germinated conidia of Aspergillus flavus and Fusarium moniliforme . These peptides were weakly lethal for germinated but not for nongerminated conidia of A. flavus . Both nongerminated and germinated conidia of F. moniliforme were susceptible to these peptides. Overall, F. moniliforme was more susceptible than A. flavus to the peptides. The peptides bound strongly to chitin, mannan, galactocerebrosides, and sphingomyelin. Binding results varied for ergosterol, cholesterol, and β1,3-glucan. This revised version was published online in August 2006 with corrections to the Cover Date.     

Natural occurrence of Fusarium species and fumonisin-production by toxigenic strains isolated from poultry feeds in Argentina

Fusarium species and fumonisin production by toxigenic strains were investigated. During 1996–1998, 158 samples of poultry feeds were collected from a factory located in the department of Río Cuarto Córdoba province, Argentina. The most common species of Fusarium were F. moniliforme (60.7%) and F. nygamai (35.4%) followed by F. semitectum, F. subglutinans, F. proliferatum, F. dlamini, F. solani, F. oxysporum and F. napiforme. Fungal counts ranged from 1 × 10³ to 8 × 10⁵ CFU/g with mean values from 1.5 × 10³ to 2.3 × 10⁵ CFU/g. The highest counts were for F. dlamini, F. subglutinans, F. moniliforme and F. nygamai. Strains of F. moniliforme, F. nygamai, and F. proliferatum were screened for their potential to produce fumonisin B₁ (FB₁), fumonisin B₂ (FB₂) and fumonisin B₃ (FB₃) in corn grain. The samples were analysed using a modified high performance liquid chromatography method. The strains assayed, 43 strains, produced three fumonisins. There was a high degree of variability in the quantities of FB₁, FB₂, and FB₃ produced. The toxin produced in highest levels by the majority of the strains was FB₁. The range of concentration varied from 5.4 to 3,991, 1.01 to 189 and 0.4 to 765 ppm per gram of corn for FB₁, FB₂ and FB₃ respectively. The toxigenic pattern of strains was normal, although two strains of F. moniliforme produced exceptionally high concentrations of FB₃ and minor concentrations of FB₂ and FB₁. This is the first report from Argentina on Fusarium species in poultry feeds and fumonisin production by these strains.This revised version was published online in October 2005 with corrections to the Cover Date.     

Production of microsclerotia of the fungal entomopathogen Metarhizium anisopliae and their potential for use as a biocontrol agent for soil-inhabiting insects

Microsclerotia (MS), overwintering structures produced by many plant pathogenic fungi, have not been described for Metarhizium anisopliae. Three strains of M. anisopliae – F52, TM109, and MA1200 – formed MS in shake flask cultures using media with varying carbon concentrations and carbon-to-nitrogen (C:N) ratios. Under the conditions of this study, all strains produced MS, compact hyphal aggregates that become pigmented with culture age, in addition to more typical blastospores and mycelia. While all strains formed desiccation tolerant MS, highest concentrations (2.7–2.9 × 10⁸ L⁻¹ liquid medium) were produced in rich media with C:N ratios of 30:1 and 50:1 by strain F52. All three strains of M. anisopliae produced similar biomass concentrations when media and growth time were compared. Strain MA1200 produced higher concentrations of blastospores than the other two strains of M. anisopliae with highest blastospore concentrations (1.6 and 4.2 × 10⁸ blastospores ml⁻¹ on days 4 and 8, respectively) in media with the highest carbon and nitrogen concentrations. Microsclerotial preparations of M. anisopliae containing diatomaceous earth survived air-drying (to <5 % moisture) with no significant loss in viability. Rehydration and incubation of air-dried MS granules on water agar plates resulted in hyphal germination and sporogenic germination to produce high concentrations of conidia. Bioassays using soil-incorporated, air-dried MS preparations resulted in significant infection and mortality in larvae of the sugar beet root maggot, Tetanops myopaeformis. This is the first report of the production of sclerotial bodies by M. anisopliae and provides a novel approach for the control of soil-dwelling insects with this entomopathogenic fungus.     

The use of solid medium to study effects of cadmium, copper and zinc on yeasts and yeast-like fungi: applicability and limitations

A defined solid medium has been used to examine the responses of Aureobasidium pullulans, Saccharomyces cerevisiae and Sporobolomyces roseus to cadmium, copper and zinc. Experiments where aliquot volumes of metal salt solutions were added to wells in the centre of agar plates revealed marked differences between these organisms. The yeast-like fungus A. pullulans was the least sensitive but S. cerevisiae was more sensitive to cadmium than zinc: the reverse was true for S. roseus. Quantitative data, which complemented the qualitative results, were obtained by measurement of metal concentrations in the plates.     

Survey of fumonisin production by Fusarium species

Fumonisins B1 (FB1) and B2 (FB2), two structurally related mycotoxins with cancer-promoting activity, were recently isolated from corn cultures of Fusarium moniliforme MRC 826. These toxins have been reported to be produced also by isolates of F. proliferatum. Contamination of foods and feeds by F. moniliforme has been associated with human esophageal cancer risk, and FB1 has been shown to be the causative agent of the neurotoxic disease leukoencephalomalacia in horses. Because of the toxicological importance of the fumonisins, the potential to produce FB1 and FB2 was determined in a study of 40 toxic Fusarium isolates representing 27 taxa in 9 of the 12 sections of Fusarium, as well as two recently described species not yet classified into sections. With the exception of one isolate of F. nygamai, fumonisin production was restricted to isolates of F. moniliforme and F. proliferatum, in the section Liseola. The F. nygamai isolate produced 605 micrograms of FB1 g-1 and 530 micrograms of FB2 g-1, and the identity of the toxins was confirmed by capillary gas chromatography-mass spectrometry. This is the first report of the production of the fumonisins by F. nygamai.     

Identity of Fusarium nygamai isolates with long and short microconidial chains from millet,sorghum and soil in Africa

Several Fusarium species have been found associated with millet and sorghum in Nigeria, Lesotho and Zimbabwe. Amongst these, some isolates were originally identified as short- and long-chained types of F. nygamai. However, there was some question as to the correct identification of the long chained types. This study reclassified some of the isolates with long microconidial chains as F. moniliforme. Morphologically, these strains do not produce chlamydospores like F. nygamai, but produce swollen hyphal cells or resistant hyphae. The isolates in this study were crossed with the mating-type tester strains of Gibberella fujikuroi (F. moniliforme and G. nygamai (F. nygamai). Of the isolates with long chains of microconidia and other characteristics of F. moniliforme, 36% crossed with mating population 'A' of G. fujikuroi. Of the isolates with characteristics of F. nygamai, 65% crossed with the testers used to produce the teleomorph of F. nygamai. Mating tests support the separation of the sample population into F. moniliforme and F. nygamai. The results of this study show that genetics can be an aid in resolving some problems in fungal taxonomy. This revised version was published online in August 2006 with corrections to the Cover Date.