过氧化物酶体与病原真菌的致病性

过氧化物酶体(Peroxisome)是一类单层膜的细胞器,普遍存在于各种真核细胞中。过氧化物酶体是丰富的酶库,含有至少50种酶类,参与生物体的多种生理代谢过程,如乙醛酸循环、脂肪酸的β-氧化及活性氧的调节等。近年来,日益增多的研究表明过氧化物酶体和病原真菌的乙醛酸循环及脂肪酸的β-氧化功能的发挥密切相关,并影响病原真菌的致病性。总结过氧化物酶体中酶的种类和功能,评述过氧化物酶体与乙醛酸循环、脂肪酸β-氧化和病原真菌致病性的关系。     

cAMP signalling in pathogenic fungi: control of dimorphic switching and pathogenicity

Morphological changes in pathogenic fungi often underlie the development of virulence and infection by these organisms. Our knowledge of the components of the cell signalling pathways controlling morphological switching has, to a large extent, come from studies of pseudohyphal growth of the model organism Saccharomyces cerevisiae, in which control is exerted via changes in the intracellular cAMP and mitogen-activated protein kinase cascades. There is evidence that pathogenic fungi also utilize these pathways to control dimorphic switching between saprobic and pathogenic forms and, as such, the elements of these pathways have potential as drug targets.     

Bioprospecting for novel oxylipins in fungi: The presence of 3-hydroxy oxylipins in Pilobolus

As previously found in various members of the Mucorales, 3-hydroxy oxylipins in Mucor genevensis are associated with the sporangia, i.e. mainly the columella structure and between aggregating sporangiospores. To determine if this phenomenon is also true in distantly related members, the mucoralean fungus Pilobolus was examined. This fungus is characterized by relatively large sub sporangial-columella structures which actively eject sporangia in a sticky liquid for attachment onto herbage surrounding its growth medium – in this case horse dung. Strikingly, this fungus produced a novel oxylipin i.e. a 3-hydroxy monounsaturated fatty acid, possibly a nonenoic acid, which is mainly associated with the sub sporangial-columella structure and aggregating sporangiospores. The specificity of the antibody against 3-hydroxy oxylipins used in immunofluorescence mapping of the mucoralean fungi, was further confirmed in the yeast, Saccharomycopsis malanga which produces 3-hydroxy palmitate in crystal form. These crystals occur between aggregating yeast cells. On the basis of the available data, we hypothesize that 3-hydroxy oxylipins probably function as adhesives, attaching fungal cells to each other or to other surfaces through entropic based hydrophobic forces and/or hydrogen bonds.     

Characterization of fungi transferred by dust storms in Kuwait and their plant pathogenicity

Dust storms carry large amounts of plant detritus and microorganisms that may cause diseases in humans, animals or plants. These storms are frequent in Kuwait throughout the year. This research was conducted to identify the fungal species carried by the dust storms in Kuwait, originating from the northwesterly direction, with emphasis on plant pathogens. Fungi were isolated from settled dust samples and identified using established microbiological and molecular approaches. Fungal isolates identified as Fusarium oxysporum from settled dust were examined for pathogenicity using a number of crop plants. In total, 17 genera of fungi were identified in the dust samples. These fungi included plant pathogens or facultative plant parasites that were transported in the dust storms as viable propagules. The most common dust-carried fungi belonged to the genera Fusarium, Alternaria, Ulocladium, Phoma, Aspergillus, Acremonium and Penicillium. The F. oxysporum isolates that had been characterized by partial 18S rRNA gene sequencing were pathogenic, causing root and stem rot in tomato, bean and cucumber, but not squash.     

Production of hemicellulases by three fungi pathogenic to sugar cane

Three fungal pathogens, Ceratocystis paradoxa (CP), Cephalosporium sacchari (CS), and Marasmius sacchari (MS) were screened for the production of hemicellulose-degrading enzymes (hemicellulases) by induction on bagasse hemicellulose B, and on a commercial preparation of hemicellulose (crude xylan). All three pathogen initially grew poorly on hemicellulose B and “crude xylan” as carbon source. Profuse growth was induced, however, by using mixtures of hemicellulose B and sucrose in the culture media for CP and CS until the organisms were capable of growing on media containing only hemicellulose B. These isolates were classified as CS₁ and CP₁. Profuse growth occurred when CS and CP were grown on carboxymethylcellulose (CMC) and also when these cultures were transferred to media containing only hemicellulose B. These isolates were classified as CS₂ and CP₂. When the above four isolates were grown on hemicellulose B as carbon source in submerged liquid culture, only CP₁ did not produce any extra-cellular hemicellulase(s), and CP₂ produced the highest yield of enzyme. CS₂ and CP₂ also produced extra-cellular CM-cellulase(s). The CP₂-culture isolate was selected for the study of conditions for the optimal production of extra-cellular hemicellulase(s). A preliminary study of the action of enzymes from CS and CP isolated on hemicellulose is reported.     

The factors of bacterial pathogenicity and their role in the development of the infectious process

The latest data concerning the characterization of the pathogenicity factors of bacteria and the evaluation of their role in the realization of definite phases of the development of the infectious process are presented. The infectious process is regarded as the result of the complicated simultaneous interaction of microorganisms and different cells and tissues of the host body. The problems of the polydeterminant character of pathogenicity factors, tho possibility of the joint action of different factors at one and the same stage of the development of the infectious process and, vice versa, the action of the same factors at different stages of the interaction of the infective agent and the susceptible host are discussed. Modern data on the genetic control of pathogenicity factors, on the localization of their genetic determinants on the chromosome and the virulence plasmids, information of pathogenicity "islets" which jointly determine the pathogenic potential of the infective agent are given. The emphasis is made on fact that the general principle of the genetic control of bacterial pathogenicity is complicated relationship between chromosomal and nonchromosomal determinants; some of them form a part of genetic pathogenicity "islets", simultaneously regulating and expressing the pathogenicity factors of the infective agent.     

Communication systems in bacteria and their role in pathogenicity

A review of the literature about the bacterial systems of regulation of expression of the genes controlled by signals generated by the bacteria themselves is given. Three types of presently known Quorum sensing systems contributing to the expression of the pathogenicity factors, infection process, and formation of biofilms by pathogenic bacteria are described. Possible mechanisms of enhanced resistance of bacteria in films to antibacterial preparations and factors of immune protection of human body are discussed. The perspectives of the development of new approaches to treatment of chronic diseases caused by the pathogens producing bacterial films are considered.     

Capsaicin-sensitive afferents and their role in gastroprotection: an update

The pivotal role of capsaicin-sensitive peptidergic sensory fibers in the maintenance of gastric mucosal integrity against injurious interventions was suggested by the authors 20 years ago. Since then substantial evidence has accumulated for the local sensory-efferent function of the released CGRP, tachykinins and NO in this gastroprotective mechanism. This overview outlines some recent achievements which shed light on new aspects and further horizons in this field. (1) Cloning the capsaicin VR-1 receptor (an ion channel-coupled receptor) and raising the VR-1 knockout mice provided a definite molecular background for the existence of capsaicin-sensitive afferents with both sensory and mediator releasing functions in the stomach. This cation channel is also sensitive to hydrogen ions. (2) VR-1 agonists (capsaicin, resiniferatoxin, piperine) protect against gastric ulcer of the rat parallel with their sensory stimulating potencies. (3) Antidromic stimulation of capsaicin-sensitive vagal and somatic afferents results in the release of CGRP, tachykinins, NO and somatostatin. Somatostatin with gastroprotective effect is released from D cells and sensory nerve endings. (4) The recent theory for the existence of spinal afferents without sensory function [P. Holzer, C.A. Maggi, Dissociation of dorsal root ganglion neurons into afferent and efferent-like neurons, Neuroscience 86 (1998) 389-398] is discussed. Data proposed to support this theory are interpreted here on the basis of a dual sensory-efferent function of VR-1 positive afferents, characterized by a frequency optimum of discharges for release vasodilatory neuropeptides below the nociceptive threshold. (5) Recent data on the effect of capsaicin in healthy human stomach are summarized. These results indicate that the gastroprotective effect of capsaicin in the human stomach involves additional mechanisms to those already revealed in the rat.     

Ophiostomatoid fungi associated withIps cembrae in Japan and their pathogenicity of Japanese larch

Six ophiostomatoid fungi, i.e.,Ceratocystiopsis minuta, Ceratocystis laricicola, Ophiostoma brunneo-ciliatum, O. laricis, O. piceae andOphiostoma sp., were isolated from the galleries ofIps cembrae on Japanese Iarch (Larix kaempferi) logs in central Honshu, Japan. Japanese larch trees approximately 30 yr old were inoculated with all six fungi.Ceratocystis laricicola produced the largest lesions on the inner bark around the inoculation point and the largest dry zone in the sapwood. Furthermore,C. laricicola was the only fungus associated withI. cembrae that had the ability to kill Japanese larch, death occurring in 30-yr-old trees within 3.5 mo after inoculation.     

Phytotoxicity of pathogenic fungi and their mycotoxins to cereal seedling viability

Aspergillus flavus, Alternaria alternata and Fusarium oxysporum were the pathogenic fungi most reduced cereal (barley, sorghum and wheat) seedlings. The pathogens have the ability to produce aflatoxin B₁ and G₁, diacetoxyscirpenol, kojic acid and tenuazonic acid that reduced seedling viability. The inhibition dose for 50% reduction (LD₅₀) was recorded by aflatoxins at 0.83 mg L^-1 for barley, 1.74 mg L^-1 for wheat and 2.75 mg L^-1 for sorghum. Diacetoxyscirpenol produced its inhibition at 1.26 mg L^-1 for barley, 3.98 mg L^-1 for wheat and 10 mg L^-1 for sorghum. Kojic acid induced 50% inhibition at 63 mg L^-1 for barley, 105 mg L^-1 for wheat and 251 mg L^-1 for sorghum. However, tenuazonic acid was less toxic where the toxicity ranged between 79–550 mg L^-1. The germination inhibition was more pronounced in barley followed by wheat and was negligible in sorghum for all tested mycotoxins. This inhibition was attributed to the reduction in the seedling amylase activity, where amylase was also reduced in the same trend: barley > wheat > sorghum. Grain treated with carboxin-captan and thiophanatemethyl-thiram at 1 g kg^-1 grain increased the seedlings vigour of wheat in sterilized soil by 45 and 22%, barley by 24 and 33% and sorghum by 15 and 30%, respectively. These fungicides also had a positive effect on cereal when the soil was inoculated with A. flavus, A. alternata and F. oxysporum, but the improvement was still below normal. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytotoxicity of pathogenic fungi and their mycotoxins to cereal seedling viability

Aspergillus flavus, Alternaria alternata and Fusarium oxysporum were found to be the pathogenic fungi mostly reducing cereal (barley, sorghum and wheat) seedlings. The pathogens have the ability to produce aflatoxin B1 and G1, diacetoxyscirpenol, kojic acid and tenuazonic acid that reduced seedling viability. The inhibition dose for 50% reduction (LD50) was recorded by aflatoxins at 0.83 mg L-1 for barley, 1.74 mg L-1 for wheat and 2.75 mg L-1 for sorghum. Diacetoxyscirpenol produced its inhibition at 1.26 mg L-1 for barley, 3.98 mg L-1 for wheat and 10 mg L-1 for sorghum. Kojic acid induced 50% inhibition at 63 mg L-1 for barley, 105 mg L-1 for wheat and 251 mg L-1 for sorghum. However, tenuazonic acid was less toxic where, the toxicity was ranged between 79-550 mg L-1. The inhibition in germination was more pronounced in barley followed by wheat and negligible in sorghum to all tested mycotoxins. This inhibition attributed to the reduction in seedling amylase activity. Amylase was also reduced in the same trend: barley > wheat > sorghum. Grain treatment with carboxin-captan and thiophanatemethyl-thiram at 1 g kg-1 grain increased seedlings vigour of wheat in sterilized soil by 45 and 22%, barley by 24 and 33% and sorghum by 15 and 30%, respectively. These fungicides have also a positive effect on cereal when soil was inoculated with A. flavus, A. alternata and F. oxysporum.     

Biosynthesis of fungal melanins and their importance for human pathogenic fungi

For more than 40 years fungi have been known to produce pigments known as melanins. Predominantly these have been dihydroxyphenylalanine (DOPA)-melanin and dihydroxynaphthalene (DHN)-melanin. The biochemical and genetical analysis of the biosynthesis pathways have led to the identification of the genes and corresponding enzymes of the pathways. Only recently have both these types of melanin been linked to virulence in some human pathogenic and phytopathogenic fungi. The absence of melanin in human pathogenic and phytopathogenic fungi often leads to a decrease in virulence. In phytopathogenic fungi such as Magnaporthe grisea and Colletotrichum lagenarium, besides other possible functions in pathogenicity, DHN-melanin plays an essential role in generating turgor for plant appressoria to penetrate plant leaves. While the function of melanin in human pathogenic fungi such as Cryptococcus neoformans, Wangiella dermatitidis, Sporothrix schenckii, and Aspergillus fumigatus is less well defined, its role in protecting fungal cells has clearly been shown. Specifically, the ability of both DOPA- and DHN-melanins to quench free radicals is thought to be an important factor in virulence. In addition, in several fungi the production of fungal virulence factors, such as melanin, has been linked to a cAMP-dependent signaling pathway. Many of the components involved in the signaling pathway have been identified.     

Survey of volatile oxylipins and their biosynthetic precursors in bryophytes

Oxylipins are metabolites which are derived from the oxidative fragmentation of polyunsaturated fatty acids. These metabolites play central roles in plant hormonal regulation and defense. Here we survey the production of volatile oxylipins in bryophytes and report the production of a high structural variety of C5, C6, C8 and C9 volatiles of mosses. In liverworts and hornworts oxylipin production was not as pronounced as in the 23 screened mosses. A biosynthetic investigation revealed that both, C18 and C20 fatty acids serve as precursors for the volatile oxylipins that are mainly produced after mechanical wounding of the green tissue of mosses.     

Manganese superoxide dismutase in pathogenic fungi: An issue with pathophysiological and phylogenetic involvements

Manganese-containing superoxide dismutases (MnSODs) are ubiquitous metalloenzymes involved in cell defence against endogenous and exogenous reactive oxygen species. In fungi, using this essential enzyme for phylogenetic analysis of Pneumocystis and Ganoderma genera, and of species selected among Ascomycota, Basidiomycota and Zygomycota, provided interesting results in taxonomy and evolution. The role of mitochondrial and cytosolic MnSODs was explored in some pathogenic Basidiomycota yeasts (Cryptococcus neoformans var. grubii, Cryptococcus neoformans var. gattii, Malassezia sympodialis), Ascomycota filamentous fungi (Aspergillus fumigatus), and Ascomycota yeasts (Candida albicans). MnSOD-based phylogenetic and pathogenic data are confronted in order to evaluate the roles of fungal MnSODs in pathophysiological mechanisms.     

Apical meristems of tomato roots and their modifications induced by arbuscular mycorrhizal and soilborne pathogenic fungi

Functional morphological patterns in root apices of tomato ( Lycopersicon esculentum ) dependent on growth, ageing and infection by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and/or by the soilborne pathogenic fungus Phytophthora nicotianae var parasitica ( P. parasitica ) were studied. Uninfected root apices were characterized by closed, tri-layered meristems with nonreticulate nuclei; however, some apices of each treatment lost their meristematic nature, stopped growing and differentiated, becoming 'parenchymatized'. The pathogenic fungus reduced the apex diameter and the number of mitotically active and viable apices inducing plasmolysis, cell and nucleus degeneration, and necrosis. The AM fungus, on the other hand, produced an increase in apex size and reduced the percentage of necrosis both in uninfected roots and in roots infected by P. parasitica . Thus, the AM fungus protected the apices from the pathogenic infection, allowing normal root growth. Furthermore, larger apices, which produce thicker roots, might indirectly contribute to plant protection. Increased volumes of colonizable tissues favour the spreading of the symbiont, and P. parasitica hyphae are always excluded from arbuscule-containing cells.     

Herbivory meets fungivory: insect herbivores feed on plant pathogenic fungi for their own benefit

Plants are regularly colonised by fungi and bacteria, but plant‐inhabiting microbes are rarely considered in studies on plant–herbivore interactions. Here we show that young gypsy moth (Lymantria dispar) caterpillars prefer to feed on black poplar (Populus nigra) foliage infected by the rust fungus Melampsora larici‐populina instead of uninfected control foliage, and selectively consume fungal spores. This consumption, also observed in a related lepidopteran species, is stimulated by the sugar alcohol mannitol, found in much higher concentration in fungal tissue and infected leaves than uninfected plant foliage. Gypsy moth larvae developed more rapidly on rust‐infected leaves, which cannot be attributed to mannitol but rather to greater levels of total nitrogen, essential amino acids and B vitamins in fungal tissue and fungus‐infected leaves. Herbivore consumption of fungi and other microbes may be much more widespread than commonly believed with important consequences for the ecology and evolution of plant–herbivore interactions.