Melanin as a virulence factor of Paracoccidioides brasiliensis and other dimorphic pathogenic fungi: a minireview

Melanin pigments are substances produced by a broad variety of pathogenic microorganisms, including bacteria, fungi, and helminths. Microbes predominantly produce melanin pigment via tyrosinases, laccases, catecholases, and the polyketide synthase pathway. In fungi, melanin is deposited in the cell wall and cytoplasm, and melanin particles (“ghosts”) can be isolated from these fungi that have the same size and shape of the original cells. Melanin has been reported in several human pathogenic dimorphic fungi including Paracoccidioides brasiliensis, Sporothrix schenckii, Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides posadasii. Melanization appears to contribute to virulence by reducing the susceptibility of melanized fungi to host defense mechanisms and antifungal drugs.     

银叶老鹳草(Geranium sylvaticum)种群中诱导保护抗性和病原菌相互作用的研究（英）

本文通过自然植物种群接种实验,人工接种实验和野外调查研究了（Geranium sylvaticum)对老鹳草单孢锈菌（Uromyces geranii)（长生活史）的抗病性在受柄锈菌（Puccinia)（短生活史）感病前后和受2种柄锈菌（P.leveillei或P.morthieri)感病后有无区别,以及在同一季节里感染同一寄主植物的长生活史单孢锈菌和短生活史柄锈菌间的相互作用,病原菌间的相互作用使寄主植物产生诱导保护抗性。结果表明,P.leveillei可诱导寄主植物产生短时间的保护抗性,而P.morthieri可能诱导寄主植物产生长时期的保护抗性,诱导保护抗性可能是影响自然植物种群中植病式样的重要因素之一。     

新疆石河子地区甜樱桃采后腐烂致病真菌的分离鉴定

【背景】甜樱桃果实柔软多汁,采后腐烂率高。石河子是新疆新兴的甜樱桃种植地区之一,但由于采后储运不当造成巨大的经济损失。【目的】鉴定石河子地区的甜樱桃果实腐烂病原菌,以期提高该地区甜樱桃的采后品质、延长货架期。【方法】从石河子136团种植的甜樱桃腐坏组织中分离真菌菌株,根据柯赫氏法则将分离得到的菌株重新接种到健康的甜樱桃果实上确定其致病性;结合形态学和真菌核糖体转录间隔区(r DNA-ITS)序列分析对致病真菌进行鉴定。【结果】从石河子地区甜樱桃腐烂的果肉中分离出5类丝状真菌,其中3类是甜樱桃果实的致病真菌,转录间隔区序列比对确定3类真菌中代表菌株分别为易脆毛霉(Mucorfragilis)、镰刀菌(Fusariumsp.)和干酪青霉(Penicillium camemberti)。【结论】导致新疆石河子地区甜樱桃果实腐烂的致病真菌主要有易脆毛霉(Mucor fragilis)、镰刀菌(Fusarium sp.)和干酪青霉(Penicillium camemberti)。     

Ecology of dermatophytes and other keratinophilic fungi in swimming pools and polluted and unpolluted streams

The biodiversity and richness of keratinophilic fungal communities including dermatophytes were assessed in three stream sites and three swimming pools in the Nablus district in Palestine, using hair baiting (HBT) and surface dilution plate (SDP) techniques, over 8- and 6-month periods, respectively. The effect of waste water effluent and selected ecological factors on these fungi in relation to species diversity and population densities were also considered. Fifty keratinophilic fungal species were recovered from the aquatic habitats studied, of which 42 were recovered from stream sites and 22 from swimming pools. Of these fungi 6 were either dermatophytes (Microsporum gypseum, and Trichophyton mentagrophytes) or dermatophyte related species (Chrysosporium merdarium, Ch. tropicum, Ch. keratinophilum and T. terrestre). The most frequently isolated species in the three pools were Acremonium strictum and Cladosporium cladosporioides, using Sabouraud dextrose agar medium (SDA). The most abundant species were Acr. strictum, and Aspergillus flavus. However, only 4 species were isolated using the SDA medium amended with 5-flurocytosine (5-FC). The most frequent and abundant species in the three stream sites using SDA medium were Geotricum candidum, and Penicillium chrysogenum. The most frequent species in the three sites using the 5-FC medium, was Paecilomyces lilacinus. Using HBT, the most abundant and frequent species in the three stream sites were G. candidum, and Pa. lilacinus, on SDA medium, and Pa. lilacinus, and Gliocladium nigrovirens on the 5-FC medium. The 5-FC medium was more suitable for the isolation of dermatophytes and closely related species than the SDA medium; 6 were recovered on 5-FC, whereas only one on the SDA medium. Variation in the levels of keratinophilic fungal populations from the three stream sites sampled 5 times over an 8-month period, followed comparable fluctuation patterns. Waste water affected fungal population densities with the highest levels in the un-polluted stream sites, and lowest in the heavily polluted sites. Swimming pools, polluted and un-polluted stream sites were found to be rich in pathogenic and potentially pathogenic fungi.This revised version was published online in October 2005 with corrections to the Cover Date.     

城市生态系统中AM真菌侵染与群落结构特征

丛枝菌根(AM)真菌作为土壤微生物的重要成员之一,对城市生态系统可持续发展具有重要意义.本文系统总结了城市生态系统中AM真菌着生状况和群落结构特点,探讨了城市生态因子,如人类行为、植被重建与维护、城市土壤状况等对AM真菌着生状况和群落结构的影响,认为今后应加强城市生态系统中AM真菌群落结构与功能的研究,如关键城市生态因子(如水资源匮乏、热岛效应等)改变AM真菌群落结构的效应与机制.     

Inter-vessel pitting and cavitation in woody Rosaceae and other vesselled plants: a basis for a safety versus efficiency trade-off in xylem transport

The hypothesis that greater safety from cavitation by air-seeding through inter-vessel pits comes at the cost of less porous pit membranes with greater flow resistance was tested . Sixteen vessel-bearing species were compared: 11 from the Rosaceae, four from other angiosperm families, and one fern. Unexpectedly, there was no relationship between pit resistance (and hence the prevailing membrane porosity) and cavitation pressure. There was, however, an inverse relationship between pit area per vessel and vulnerability to cavitation (r² = 0.75). This suggests that cavitation is caused by the rare largest membrane pore per vessel, the average size of which increases with total pit area per vessel. If safety from cavitation constrains pit membrane surface area, it also limits vessel surface area and the minimum vessel resistivity. This trade-off was consistent with an approximately three-fold increase in vessel resistivity with cavitation pressure dropping from −0.8 to −6.6 MPa. The trade-off was compensated for by a reduction in the percentage of vessel wall pitted: from 10–16% in vulnerable species to 2–4% in resistant species. Across species, end-wall pitting accounted for 53 ± 3% of the total xylem resistivity. This corresponded to vessels achieving on average 94 ± 2% of their maximum possible conductivity if vessel surface area is constrained.     

Differentiations of determinants for the community compositions of bacteria,fungi, and nitrogen fixers in various steppes

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Environment factors influence in vitro interspecific interactions between A. ochraceus and other maize spoilage fungi,growth and ochratoxin production

The effect of water availability (water activity,a_w; 0.995–0.90) and temperature (18–30 °) on in vitro interactions between an ochratoxin producing strain of Aspergillus ochraceus and six other spoilage fungi was assessed in dual culture experiments on a maize meal-based agar medium. Inprimary resource capture of nutrient substrate, A. ochraceus was dominant against many of the interacting species, being able to overgrow and replace A. candidus, and sometimes A. flavus and the Eurotium spp. regardless of a_w or temperature. However, with freely available water (0.995 a_w) A. alternata and A. niger were dominant, with mutual antagonism between A. ochraceus and A. flavus at 25–30 °C. In the driest conditions tested (0.90 a_w) there was also mutual antagonism between A. ochraceus and the two Eurotium spp. Overall, under allconditions tested the Index of Dominance for A. ochraceus was much higher than for other competing species combined suggesting that A. ochraceus wasa good competitive colonist able to replace a numberof other species. However, the growth rate ofA. ochraceus was modified and decreased by the interaction with competitors. Interaction between A. ochraceus and species such as A. alternata (18°C/0.995) and Eurotium spp. (0.995–0.95 and 25–30 °C) resulted in a significant stimulation of ochratoxin production. Theresults are discussed in relation to the effect that environmental factors have on the possible competitiveness of A. ochraceus in the maizegrain ecosystem and the role of ochratoxin in nicheexclusion of competitors. This revised version was published online in June 2006 with corrections to the Cover Date.     

寒温带地区典型森林类型中外生菌根真菌多样性和群落组成及其影响因素

外生菌根(ECM)真菌可促进宿主植物对土壤中水分和营养的吸收,提高宿主植物的抗逆性及对环境的适应,在森林生态系统的物质循环中发挥了重要作用。为探明寒温带地区ECM真菌多样性和群落组成以及土壤理化因子对真菌群落组成的可能影响机制,采用高通量测序(Illumina Miseq)平台对大兴安岭4种典型森林类型白桦、樟子松、兴安落叶松和偃松的根围土壤ECM真菌群落组成进行了分析。结果表明,4种典型森林类型根围土壤中共获得167个ECM真菌可操作分类单元(OTUs),隶属于2个门、4个纲、10个目、24个科、36个属。在门水平上,担子菌门(Basidiomycota)真菌的相对丰度占96.4%,子囊菌门(Ascomycota)真菌占3.6%。在属水平上,红菇属(Russula,30.2%)、丝膜菌属(Cortinarius,17.1%)、Piloderma(9.6%)、棉革菌属(Tomentella,7.2%)、丝盖伞属(Inocybe,7.2%)和蜡壳耳属(Sebacina,6.2%)的相对丰度均>5.0%,是该地区的优势ECM真菌类群。不同森林类型的优势ECM真菌在属水平上的组成存在显...     

LaeA在丝状真菌次级代谢、生长发育和其他重要生物过程中的作用

LaeA是在构巢曲霉中首次鉴定的一种全局调控因子,其同源蛋白在丝状真菌中广泛存在,具有高度的保守性。LaeA及其同源蛋白序列存在S-腺苷甲硫氨酸结合基序,是一种甲基转移酶,可能影响组蛋白修饰,导致染色体结构的改变,进而调控一系列基因的表达。大量研究表明,LaeA及其同源蛋白参与调控丝状真菌多种次级代谢产物的生物合成,影响丝状真菌的生长发育和形态分化,甚至在丝状真菌生产有机酸和一些工业酶的过程中也发挥着重要作用。本文综述了LaeA及其同源蛋白的作用机制,以及该蛋白在丝状真菌次级代谢、生长发育和其他重要生物过程中的作用,并对存在的问题及应用前景进行讨论与展望。     

Drinking water quality and risk implications for community health: A case study of shallow water wells and boreholes in three major communities in Northern Cross-River,Southern Nigeria

The quality of water sources and its potential health implications to adults and children populations of respective major communities in Northern Cross-River was assessed. Water samples (n = 10/water source/site) were collected from three (Okpoma, Okuku and Ugaga) communities and heavy metal concentrations (Lead (Pb), Cadmium (Cd), Chromium (Cr), Manganese (Mn), Nickel (Ni), Copper (Cu), Cobalt (Co), and Zinc (Zn)) were evaluated using Atomic Absorption Spectrometer (AAS). Overall, Pb, Cd, Ni, and Co were higher than drinking water guidelines, while only Cr, Mn, Cu, and Zn were within the permissible limits. The estimated average daily intake (EADI) and target hazard quotient (THQ) were used to determine risk implications for adult and children consumer populations. The EADI for Pb in adults for borehole water, Pb and Cr by child consumer population for borehole and shallow well water exceeded the reference dose (RfD) by USEPA. The THQ for adult population were >1 for Pb in borehole water and >1 for Pb and Cr across all sites for the child consumer population. Overall, our findings indicate toxicity and higher hazard risk for both adult (Pb) and children (Pb and Cr) populations that source drinking water from borehole and shallow well water in these communities.     

Flavonoids in roots of white clover: interaction of arbuscular mycorrhizal fungi and a pathogenic fungus

The effects of two arbuscular mycorrhizal fungi (AMF) (Glomus mosseae and G. claroideum) and a pathogenic fungus (Pythium ultimum) on the production of eight flavonoids in roots of two white clover (Trifolium repens L.) cultivars were evaluated. Quantification of AM and pathogenic fungi in the roots showed that the AM symbiosis significantly reduced P. ultimum biomass and in some cases prevented infection. The flavonoid productions in clover roots varied depending on the presence of beneficial and/or pathogenic fungi, fungal isolate or plant cultivar. Only plants colonized with G. claroideum showed detectable concentrations of either coumestrol or kaempferol (cultivar-dependant). In addition, inoculation with G. claroideum resulted in significantly higher concentrations of coumestrol in cv. Sonja and medicarpin in cv. Milo. A low production of coumestrol and kaempferol in mycorrhizal plants may be G. mosseae-specific. Only the concentrations of formononetin and daidzein increased in clover roots in response to infection with P. ultimum. These flavonoids are supposedly stress metabolites, synthesized or produced from glycosides in response to pathogen infection. However, the presence of one or both AMF significantly lowered the formononetin and daidzein concentrations, and overruled the inductive effect of P. ultimum. Therefore the antagonistic action of AM against the pathogen must take place through another mechanism.     

Twenty years of research on community composition and species distribution of arbuscular mycorrhizal fungi in China: a review

The biodiversity and distribution of arbuscular mycorrhizal fungi (AMF) in different ecosystems and plant communities in China has received increasing interest over the past decades. This has led to a steady increase in the number of scientific papers published on this topic. Studies have surveyed AMF-colonizing rhizospheres of most families of angiosperms, bryophytes, pteridophytes, and gymnosperms. China has about 30,000 plant species (one eighth of the plant species worldwide). A total of 104 AMF species within nine genera, including 12 new species, have been reported in environments such as croplands, grasslands, forests, and numerous disturbed environments. In this paper, we review data published over the past 20 years on AMF community composition and species distribution, the mycorrhizal status of plants, AMF spore communities in different habitats, and germplasm collections in China. Possible future trends in the study of the biodiversity of AMF are also briefly discussed. In particular, the aim of our review is to make some of the recent work published in the Chinese literature accessible to a wider international audience.     

Impact of a Streptomyces (AS1) strain and its metabolites on control of Aspergillus flavus and aflatoxin B1 contamination in vitro and in stored peanuts

Six actinomycetes were isolated from peanuts in Egypt. Of these, a Streptomyces strain (AS1) was found in in vitro assays to inhibit directly or via secondary metabolites both germination and growth of Aspergillus flavus. Tests of the AS1 cells for direct control of A. flavus populations or aflatoxin B₁ (AFB₁) production on stored peanuts was unsuccessful over 14-day storage periods. However, crude extracts of AS1 metabolites at 50 and 100 ppm completely inhibited spore germination of conidia of A. flavus in vitro over 48 h. Comparison of solvents for extracting the metabolites showed that the ethyl acetate extract was most effective. This gave greater than 85% inhibition of mycelial growth at these concentrations at different water availabilities (water activity; a _w; 0.95, 0.92, and 0.89) and 25°C. Doses of 50, 200, and 500 ppm of AS1 metabolites significantly inhibited populations of A. flavus on stored peanuts at two water stress levels (0.90, 0.93 a _w) at 25°C over 14-day storage periods. The amounts of AFB₁ produced by A. flavus on peanuts stored at 0.90 a _w were significantly decreased by AS1 metabolites for only 7 days. However, at 0.93 a _w doses of 200 and 500 ppm significantly controlled AFB₁ accumulation in peanuts for 14 days.     

Patterns of community composition and diversity in latent fungi of living Quercus serrata trunks across a range of oak wilt prevalence and climate variables in Japan

Given that forest dieback due to emerging pests is increasing under global warming, understanding the relationships between pests, climate, and forest biodiversity is an urgent priority. In Japan, mass attacks of an ambrosia beetle, vectoring a pathogenic fungus, cause oak wilt outbreaks in recent decades. Here, the associations of oak wilt and climate with wood-inhabiting fungal communities in apparently healthy Quercus serrata trunks were investigated using DNA metabarcoding in seven sites along a climatic gradient in Japan. Amplicon sequencing of the fungal internal transcribed spacer 1 region generated 1,339,958 sequence reads containing 879 fungal operational taxonomic units (OTUs) in 234 wood samples. OTU compositions were significantly different between sites with and without oak wilt. OTU richness increased with temperature and precipitation at sites where oak wilt was present, but this relationship was not observed at sites without oak wilt, possibly due to interaction between oak wilt and climate.     

A survey of soils for aggregate stability and glomalin,a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi

Understanding the contributions of soil microorganisms to soil stabilization at the molecular level will lead to ways to enhance inputs for sustainable agricultural systems. Recent discoveries of copious production of glycoprotein (glomalin) by arbuscular mycorrhizal (AM) fungi and the apparent recalcitrance of this material in soils led to the comparison between concentration of glomalin and aggregate stability. Stability was measured on air-dried aggregates rewetted by capillary action and then subjected to wet sieving for 10 min. Thirty-seven samples from four geographic areas of the U.S. and one area of Scotland were tested. The monoclonal antibody used to discover glomalin on AM hyphae was employed to assess immunoreactive glomalin on aggregate surfaces by immunofluorescence and in extracts from aggregates by enzyme-linked immunosorbent assay (ELISA). Immunofluorescence was observed on at least some surfaces of aggregates from all soils examined, but was most evident on aggregates with high glomalin concentrations. Easily extractable glomalin (EEG) was solubilized by 20 mM citrate, pH 7.0 at 121 °C for 30 min, and total glomalin (TG) was solubilized with 50 mM citrate, pH 8.0 at 121 °C for 90 to 450 min. Some soils required up to seven sequential extractions to remove all of the glomalin. Aggregate stability was linearly correlated (p < 0.001) with all measures of glomalin (mg/g of aggregates) in these soils. The best predictor of aggregate stability (AS) was immunoreactive easily extractable glomalin (IREEG) according to the following relationship: AS = 42.7 +61.3 × log₁₀ IREEG (r₂ = 0.86; p <0.001, n = 37).     

High disease incidence and apparent disease tolerance in a North American Great Basin plant community

Patterns and consequences of plant disease at the community level have rarely been studied. We surveyed fungal infection in a Great Basin community of perennial shrubs over 4 years. Repeat surveys in fixed plots and along transects showed that disease incidence in the dominant perennial species was often very high, with up to 100% of all individuals infected. Despite the widespread prevalence of infection, and its severity on individual plants (which sometimes had over 1/3 of their leaves covered in pustules), its effects on survival and flowering were undetectably small. Thus, this perennial community appears to be stable, despite widespread disease. There are two potential explanations for this pattern; either the pathogens have evolved to be avirulent, or the hosts have become tolerant to being infected. Avirulence is not likely, because multiple infections are common in this system, and multiple infections have been shown in other species to favor strains that are faster reproducing and thus more virulent. Instead, it is more likely that tolerance has evolved in these host species, because infection in each year is practically inevitable and because the host plants are long-lived, giving little opportunity for new resistance genotypes to evolve. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nitrogen content, amino acid composition and digestibility of fungi from a nutritional perspective in animal mycophagy

Fungi comprise a major part of the diet of many animals. Even so, the nutritional value of fungi has been much debated, with some arguing that fungi are nutritionally poor. However, the chemical composition of fungi and of the biology of the animals that eat them are not well understood, particularly in reference to amino acid (AA) composition of fungi and digestibility of fungal protein. We analysed fibre, total nitrogen (N), available N, and AA contents and measured in vitro digestibility of a wide range of epigeous and hypogeous fungi collected in Australia and the USA to test three hypotheses: (i) fungi are nutritionally poor because they contain few nutrients or are otherwise of low digestibility, (ii) fungi vary substantially in their nutritional composition; and (iii) animals can counter this variable quality by eating diverse taxa. Resultant data indicate many fungi are a reasonable source of AAs and digestible nitrogen. However, they vary highly between species in AA content, and the protein has a poor balance of digestible AAs. This helps explain why many mycophagous animals eat a wide array of fungi and often have digestive strategies to cope with fungi, such as foregut fermentation. Another common strategy is to supplement the diet with high quality protein, such as insect protein. Accordingly, evaluating nutritional value of fungi requires consideration of physiology of the animal species and their whole diet.