Isolation, activity and immunological characterisation of a secreted aspartic protease, CtsD, from Aspergillus fumigatus

Aspergillus fumigatus is an opportunistic fungal pathogen that infects immunocompromised patients. A putative aspartic protease gene (ctsD; 1425 bp; intron-free) was identified and cloned. CtsD is evolutionarily distinct from all previously identified A. fumigatus aspartic proteases. Recombinant CtsD was expressed in inclusion bodies in Escherichia coli (0.2mg/g cells) and subjected to extensive proteolysis in the baculovirus expression system. Activation studies performed on purified, refolded, recombinant CtsD resulted in protease activation with a pH(opt)4.0 and specific activity=10 U/mg. Pepstatin A also inhibited recombinant CtsD activity by up to 72% thereby confirming classification as an aspartic protease. Native CtsD was also immunologically identified in culture supernatants and purified from fungal cultures using pepstatin-agarose affinity chromatography (7.8 microg CtsD/g mycelia). In A. fumigatus, semi-quantitative RT-PCR analysis revealed expression of ctsD in minimal and proteinaceous media only. Expression of ctsD was absent under nutrient-rich conditions. Expression of ctsD was also detected, in vivo, in the Galleria mellonella virulence model following A. fumigatus infection.     

Antifungal activity of microbial secondary metabolites

Secondary metabolites are well known for their ability to impede other microorganisms. Reanalysis of a screen of natural products using the Caenorhabditis elegans-Candida albicans infection model identified twelve microbial secondary metabolites capable of conferring an increase in survival to infected nematodes. In this screen, the two compound treatments conferring the highest survival rates were members of the epipolythiodioxopiperazine (ETP) family of fungal secondary metabolites, acetylgliotoxin and a derivative of hyalodendrin. The abundance of fungal secondary metabolites indentified in this screen prompted further studies investigating the interaction between opportunistic pathogenic fungi and Aspergillus fumigatus, because of the ability of the fungus to produce a plethora of secondary metabolites, including the well studied ETP gliotoxin. We found that cell-free supernatant of A. fumigatus was able to inhibit the growth of Candida albicans through the production of a secreted product. Comparative studies between a wild-type and an A. fumigatus ΔgliP strain unable to synthesize gliotoxin demonstrate that this secondary metabolite is the major factor responsible for the inhibition. Although toxic to organisms, gliotoxin conferred an increase in survival to C. albicans-infected C. elegans in a dose dependent manner. As A. fumigatus produces gliotoxin in vivo, we propose that in addition to being a virulence factor, gliotoxin may also provide an advantage to A. fumigatus when infecting a host that harbors other opportunistic fungi.     

Gene expression profiling of polymorphonuclear leukocytes treated with the culture filtrate of Aspergillus fumigatus and gliotoxin

Pathogens of the Aspergillus species are frequently seen in deep-seated mycoses. We previously demonstrated that the culture filtrate of Aspergillus fumigatus (CF) has immunosuppressive effects on polymorphonuclear leukocytes (PMNs), which act as the main phagocytes to hyphae of Aspergillus fumigatus (A. fumigatus). But little is known about the gene expression profiles involved in it. Therefore we investigated the changes in gene expression in human PMNs treated with CF or gliotoxin at two time points, using microarray analysis. CF and gliotoxin changed the expression of 548 and 381 genes, respectively. Only 51 genes showed the same expression patterns with the two stimulants, and CF-induced changes in gene expression occurred comparatively earlier than those induced by gliotoxin. Among 31 genes encoding apoptosis, which were up- or down-regulated in this assay, only 3 genes were similarly changed by both kinds of stimulation. Apoptosis was detected and quantified using two apoptosis assays. CF and gliotoxin changed the expessions of only 3 out of 19 regulated genes related to inflammatory mediators and receptors similarly. The up-regulation of the gene encoding annexin 1 (ANXA1), which is known to be involved in extravasation and apoptosis of neutrophils, may play a role in the immunosuppressive effect of A. fumigatus. The difference in expression changes between CF and gliotoxin is presumed to be caused by the interaction among the components of CF and therefore the interaction is an area of interest for further investigation.     

Cytotoxic Substances from Aspergillus fumigatus in Oxygenated or Poorly Oxygenated Environment

Aspergillus fumigatus often causes serious health problems. The airway of the human body, the most common initial site of damage, is always exposed to an oxygenated condition, and the oxygen concentration may play a critical role in the virulence of A. fumigatus. In this study, oxygen content, fungal growth, the production of cytotoxic substance(s) in the fungal culture, and their relationship were investigated. Two clinical strains of A. fumigatus were cultured under certain oxygen contents (10, 14 and 20%), and cytotoxicity of their culture filtrates on murine macrophages and their fungal growth were evaluated. The components of these filtrates were analyzed by gas chromatography-mass spectrometry. All culture filtrates contained gliotoxin and showed potent cytotoxicity on macrophages at very low concentration. The amount of gliotoxin in the culture filtrate prepared at 10% oxygen was markedly less, but diminutions in fungal growth and cytotoxicity of this culture filtrate were negligible. These results suggest that a well-oxygenated condition is suitable for the production of gliotoxin by A. fumigatus. A significant role of cytotoxic substances(s) other than gliotoxin is also suggested.     

Bioinformatic and expression analysis of the putative gliotoxin biosynthetic gene cluster of Aspergillus fumigatus

Gliotoxin is a secondary metabolite produced by several fungi including the opportunistic animal pathogen Aspergillus fumigatus. It is a member of the epipolythiodioxopiperazine (ETP) class of toxins characterised by a disulphide bridged cyclic dipeptide. A putative cluster of 12 genes involved in gliotoxin biosynthesis has been identified in A. fumigatus by a comparative genomics approach based on homology to genes from the sirodesmin (another ETP) biosynthetic gene cluster of Leptosphaeria maculans. The physical limits of the cluster in A. fumigatus have been defined by bioinformatics and by identifying the genes that are co-regulated and whose timing of expression correlates with the production of gliotoxin in culture.     

Disruption of a nonribosomal peptide synthetase in Aspergillus fumigatus eliminates gliotoxin production

The fungal secondary metabolite gliotoxin produced by Aspergillus fumigatus has been hypothesized to be important in the development of invasive aspergillosis. In this study, we addressed this hypothesis by disrupting a nonribosomal peptide synthetase (NRPS) (encoded by gliP) predicted to be involved in gliotoxin production. Mutants with a disrupted gliP locus failed to produce gliotoxin, which confirmed the role of the NRPS encoded by gliP in gliotoxin biosynthesis. We found no morphological, developmental, or physiological defects in DeltagliP mutant strains. In addition, disruption of gliP resulted in down regulation of gene expression in the gliotoxin biosynthesis gene cluster, which was restored with addition of exogenous gliotoxin. This interesting result suggests a role for gliotoxin in regulating its own production. Culture filtrates from the DeltagliP mutant were unable to inhibit ionomycin-dependent degranulation of mast cells, suggesting a role for gliotoxin in suppressing mast cell degranulation and possibly in disease development. However, the DeltagliP mutant did not have an impact on survival or tissue burden in a murine inhalational model of invasive aspergillosis. This result suggests that gliotoxin is not required for virulence in an immunosuppressed host with an invasive pulmonary infection.     

Isolation and identification of Aspergillus fumigatus mycotoxins on growth medium and some building materials

Genotoxic and cytotoxic compounds were isolated and purified from the culture medium of an indoor air mold, Aspergillus fumigatus. One of these compounds was identified as gliotoxin, a known fungal secondary metabolite. Growth of A. fumigatus and gliotoxin production on some building materials were also studied. Strong growth of the mold and the presence of gliotoxin were detected on spruce wood, gypsum board, and chipboard under saturation conditions.     

小鼠烟曲霉角膜炎的实验研究

目的 比较伊曲康唑和氟康唑对烟曲霉的体外抗菌活性,观察伊曲康唑对小鼠烟曲霉角膜炎的治疗作用.方法 通过角膜基质注射法建立烟曲霉角膜炎小鼠模型.造模后观察角膜病变,取角膜病变处分泌物做真菌镜检、真菌培养以证实造模成功.用药基法检测伊曲康唑和氟康唑对烟曲霉的最低抑菌浓度( MIC)和最低杀菌浓度(MFC).对烟曲霉角膜炎小鼠给予伊曲康唑治疗,治疗结束行临床评分、炎性评分、菌落形成单位测定以评价疗效.结果 伊曲康唑对烟曲霉的MIC和MFC分别为6.25 μg/mL、12.5 μg/mL;氟康唑对烟曲霉的MIC和MFC分别为500 μg/mL、1 000 μg/mL.伊曲康唑治疗组临床评分、炎性评分和测定的菌落数较对照组均明显减少(P＜0.05).结论 伊曲康唑对烟曲霉的体外抗菌活性优于氟康唑,并且对烟曲霉性角膜炎有明显疗效.     

Aspergillus fumigatus toxicity and gliotoxin levels in feedstuff for domestic animals and pets in Argentina

Aims:  To evaluate gliotoxin production by Aspergillus fumigatus strains isolated from feedstuff intended for domestic animals and pets, and to determine the amount of gliotoxin in these substrates.
Methods and Results:  A total of 150 feedstuff samples were collected. They were composed of 30 samples each of five different feed types (pigs, poultry, cattle, horse and pets). Aspergillus fumigatus gliotoxin production ability and gliotoxin presence in feedstuff was determined by HPLC. Aspergillus fumigatus strains were isolated from all of the tested samples. Strains from cattle, horses and pet food were able to produce gliotoxin. Corn silage samples intended for cattle did not show gliotoxin contamination. All the other tested samples had gliotoxin levels ranging from 29 to 209 μg g⁻¹. Horse and poultry feed samples had the greatest contamination frequency.
Conclusions:  Feed samples contaminated with gliotoxin are potentially toxic to animals.
Significance and Impact of the Study:  The presence of gliotoxin could affect animal productivity and health. Moreover, there are risks of contamination to farm workers handling improperly stored animal feed. Aspergillus fumigatus strains isolated from different sources should be investigated to determine prevention and control strategies.     

Ag/TiO2纳米材料对烟曲霉的抑制作用及机制

目的 合成Ag/TiO2纳米材料,对其进行表征测定,并探讨其对烟曲霉的抑制作用及具体机制。方法 采用光催化还原法制备Ag/TiO2纳米材料,紫外可见分析和扫描电镜对其进行表征测定;微量液基稀释法检测对烟曲霉的最低抑菌浓度（MIC）,以及生物量的抑制作用;ELISA试剂盒检测对真菌谷胱甘肽还原酶、总谷胱甘肽、线粒体膜电位的影响,荧光显微镜检测活性氧的产生。结果 成功制备Ag/TiO2纳米材料,分布均匀;对烟曲霉的MIC值为0.5 μg/mL,能完全抑制烟曲霉生物量,与单独纳米银相比,具有更好的抗菌活性。机制研究发现其主要通过降低烟曲霉体内谷胱甘肽及其还原酶的含量,诱导过量活性氧的产生,最终导致线粒体膜电位降低,使真菌细胞发生凋亡。结论 Ag/TiO2纳米材料可有效阻断烟曲霉等真菌在空气中的传播,具有广泛的应用前景。     

Detection of Aspergillus fumigatus mycotoxins: immunogen synthesis and immunoassay development

Immunological detection of secreted low molecular weight toxins represents a potentially novel means of diagnosing infection by the fungus Aspergillus fumigatus. Two such metabolites, gliotoxin and helvolic acid, were selected and conjugated to thyroglobulin for antisera generation in rabbits. Gliotoxin was initially activated using N-[p-maleimidophenyl] isocyanate (PMPI) and subsequently conjugated to S-acetyl thioglycolic acid N-hydroxysuccinimide-activated thyroglobulin, whereas helvolic acid was activated with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) in the presence of thyroglobulin prior to immunisation. To facilitate subsequent antisera evaluation, both toxins were similarly conjugated to bovine serum albumin (BSA). Matrix-Assisted Laser Desorption Ionisation-Time Of Flight (MALDI-TOF) mass spectrometry and SDS-PAGE analysis confirmed covalent attachment of toxins to BSA in the ratios of 15 and 2.4 mol per mol BSA for gliotoxin and helvolic acid, respectively. Resultant high titer antisera were capable of detecting both BSA-conjugated toxins (inhibitory concentration (IC)(50): 4-5 microg/ml). Free toxins were also detectable by competitive immunoassay, whereby 10 microg/ml free gliotoxin (30 microM) and helvolic acid (17 microM), respectively, inhibited antibody binding to cognate toxin-BSA previously immobilised on microwells. This work confirms that sensitive and specific antisera can be raised against fungal toxins and may have an application in diagnosing fungal infection.     

A nonribosomal peptide synthetase (Pes1) confers protection against oxidative stress in Aspergillus fumigatus

Aspergillus fumigatus is an important human fungal pathogen. The Aspergillus fumigatus genome contains 14 nonribosomal peptide synthetase genes, potentially responsible for generating metabolites that contribute to organismal virulence. Differential expression of the nonribosomal peptide synthetase gene, pes1, in four strains of Aspergillus fumigatus was observed. The pattern of pes1 expression differed from that of a putative siderophore synthetase gene, sidD, and so is unlikely to be involved in iron acquisition. The Pes1 protein (expected molecular mass 698 kDa) was partially purified and identified by immunoreactivity, peptide mass fingerprinting (36% sequence coverage) and MALDI LIFT-TOF/TOF MS (four internal peptides sequenced). A pes1 disruption mutant (delta pes1) of Aspergillus fumigatus strain 293.1 was generated and confirmed by Southern and western analysis, in addition to RT-PCR. The delta pes1 mutant also showed significantly reduced virulence in the Galleria mellonella model system (P < 0.001) and increased sensitivity to oxidative stress (P = 0.002) in culture and during neutrophil-mediated phagocytosis. In addition, the mutant exhibited altered conidial surface morphology and hydrophilicity, compared to Aspergillus fumigatus 293.1. It is concluded that pes1 contributes to improved fungal tolerance against oxidative stress, mediated by the conidial phenotype, during the infection process.     

The Aspergillus fumigatus Protein GliK Protects against Oxidative Stress and Is Essential for Gliotoxin Biosynthesis

The function of a number of genes in the gliotoxin biosynthetic cluster (gli) in Aspergillus fumigatus remains unknown. Here, we demonstrate that gliK deletion from two strains of A. fumigatus completely abolished gliotoxin biosynthesis. Furthermore, exogenous H₂O₂ (1 mM), but not gliotoxin, significantly induced A. fumigatus gliK expression (P = 0.0101). While both mutants exhibited significant sensitivity to both exogenous gliotoxin (P < 0.001) and H₂O₂ (P < 0.01), unexpectedly, exogenous gliotoxin relieved H₂O₂-induced growth inhibition in a dose-dependent manner (0 to 10 μg/ml). Gliotoxin-containing organic extracts derived from A. fumigatus ATCC 26933 significantly inhibited (P < 0.05) the growth of the ΔgliK²⁶⁹³³ deletion mutant. The A. fumigatus ΔgliK²⁶⁹³³ mutant secreted metabolites, devoid of disulfide linkages or free thiols, that were detectable by reverse-phase high-performance liquid chromatography and liquid chromatography-mass spectrometry with m/z 394 to 396. These metabolites (m/z 394 to 396) were present at significantly higher levels in the culture supernatants of the A. fumigatus ΔgliK²⁶⁹³³ mutant than in those of the wild type (P = 0.0024 [fold difference, 24] and P = 0.0003 [fold difference, 9.6], respectively) and were absent from A. fumigatus ΔgliG. Significantly elevated levels of ergothioneine were present in aqueous mycelial extracts of the A. fumigatus ΔgliK²⁶⁹³³ mutant compared to the wild type (P < 0.001). Determination of the gliotoxin uptake rate revealed a significant difference (P = 0.0045) between that of A. fumigatus ATCC 46645 (9.3 pg/mg mycelium/min) and the ΔgliK⁴⁶⁶⁴⁵ mutant (31.4 pg/mg mycelium/min), strongly suggesting that gliK absence and the presence of elevated ergothioneine levels impede exogenously added gliotoxin efflux. Our results confirm a role for gliK in gliotoxin biosynthesis and reveal new insights into gliotoxin functionality in A. fumigatus.     

Bioprospection of Cytotoxic Compounds in Fungal Strains Recovered from Sediments of the Brazilian Coast

The cytotoxic activities of extracts (50 μg/ml) from 48 fungal strains, recovered from sediments of Pecém's offshore port terminal (Northeast coast of Brazil), against HCT‐116 colon cancer cell lines were investigated. The most promising extract was obtained from strain BRF082, identified as Dichotomomyces cejpii by phylogenetic analyses of partial RPB2 gene sequence. Thus, it was selected for bioassay‐guided isolation of the cytotoxic compounds. Large‐scale fermentation of BRF082 in potato dextrose broth, followed by chromatographic purification of the bioactive fractions from the liquid medium, yielded gliotoxin ( 4 ) and its derivatives acetylgliotoxin G ( 3 ), bis(dethio)bis(methylsulfanyl)gliotoxin ( 1 ), acetylgliotoxin ( 5 ), 6‐acetylbis(dethio)bis(methylsulfanyl)gliotoxin ( 2 ), besides the quinazolinone alkaloid fiscalin B. All isolated compounds were tested for their cytotoxicities against the tumor cell lines HCT‐116, revealing 4 and 3 as the most cytotoxic ones (IC₅₀ 0.41 and 1.06 μg/ml, resp.).     

致病菌烟曲霉新基因Afu4g13170生孢致毒相关性初步研究

【目的】对烟曲霉Afu4g13170基因功能进行初步研究。【方法】利用Double-jointPCR方法和一步基因敲除技术,构建Afu4g13170基因缺失突变株。【结果】序列比对表明烟曲霉Afu4g13170蛋白与构巢曲霉Ani04163蛋白和新型隐球菌Gib2蛋白的氨基酸序列相似性为88.6%;表型分析表明基因破坏使突变株生长迟缓、梗基伸长、孢子分化能力下降,产孢推迟、产孢量减少,色素产生量降低;色谱分析显示基因缺失突变株的产毒能力下降。【结论】烟曲霉Afu4g13170基因可以作为控制曲霉致毒的一个靶位点。     

Cytotoxicity of Aspergillus fungi isolated from hospital environment

The majority of mycotoxins produced by Aspergillus fungi are immunosuppressive agents, and their cytotoxicity may impair defense mechanisms in humans. The objective of the study was evaluation of the cytotoxicity of fungi isolated from an environment where inpatients with impaired immunity were present. The materials comprised 57 fungal strains: Aspergillus fumigatus, Aspergillus niger: Aspergillus ochraceus, Aspergillus flavus, Aspergillus versicolor and Aspergillus ustus isolated from hospital rooms in Cracow. The cytotoxicity of all the strains was evaluated using the MTT test (3-(4,5-dimethylthiazol-2-yl) 2,5 diphenyltetrazolium bromide). To emphasize the differences in cytotoxicity among the particular strains, variance analysis (ANOVA) and Tukey's difference test were used. Out of 57 Aspergillus strains tested, 48 (84%) turned out to be cytotoxic. The cytyotoxicity was high (+++) in 21 strains, mainly in A. fumigatus. The least cytotoxic were A. niger fungi, this being statistically significant (p<0,05). To protect a patient from the adverse effects of mycotoxins, not only his or her immunity status should be evaluated but also the presence of fungi in hospital environment and their cytotoxicity should be monitored (possible exposure).     

Gliotoxin in <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis>: an example that mycotoxins are potential virulence factors

Moulds produce several different mycotoxins that may improve their chance of survival in particular environments. For example, Aspergillus fumigatus, an important human pathogen, produces several mycotoxins including gliotoxin. This secondary metabolite, a small lipid soluble dipeptide, exerts toxic effects on phagocytic cells and T-lymphocytes at low concentrations in vitro. A. fumigatus also produces high levels of gliotoxin in vivo, and this suggests that host defense mechanisms might be impaired by this metabolite during host infection. In the past few years, the genes responsible for the production of gliotoxin in A. fumigatus have been identified and more recently gliotoxin-minus mutants have been used in animal experiments to ascertain the biological role of this product. Mycotoxins have also been shown to act as virulence factors in some fungal infections of insects and plants.