A novel C2H2 transcription factor that regulates gliA expression interdependently with GliZ in Aspergillus fumigatus.

Secondary metabolites are produced by numerous organisms and can either be beneficial, benign, or harmful to humans. Genes involved in the synthesis and transport of these secondary metabolites are frequently found in gene clusters, which are often coordinately regulated, being almost exclusively dependent on transcription factors that are located within the clusters themselves. Gliotoxin, which is produced by a variety of Aspergillus species, Trichoderma species, and Penicillium species, exhibits immunosuppressive properties and has therefore been the subject of research for many laboratories. There have been a few proteins shown to regulate the gliotoxin cluster, most notably GliZ, a Zn2Cys6 binuclear finger transcription factor that lies within the cluster, and LaeA, a putative methyltransferase that globally regulates secondary metabolism clusters within numerous fungal species. Using a high-copy inducer screen in A. fumigatus, our lab has identified a novel C2H2 transcription factor, which plays an important role in regulating the gliotoxin biosynthetic cluster. This transcription factor, named GipA, induces gliotoxin production when present in extra copies. Furthermore, loss of gipA reduces gliotoxin production significantly. Through protein binding microarray and mutagenesis, we have identified a DNA binding site recognized by GipA that is in extremely close proximity to a potential GliZ DNA binding site in the 5' untranslated region of gliA, which encodes an efflux pump within the gliotoxin cluster. Not surprisingly, GliZ and GipA appear to work in an interdependent fashion to positively control gliA expression.

Plasmids for increased efficiency of vector construction and genetic engineering in filamentous fungi.

Fungal species are continuously being studied to not only understand disease in humans and plants but also to identify novel antibiotics and other metabolites of industrial importance. Genetic manipulations, such as gene deletion, gene complementation, and gene over-expression, are common techniques to investigate fungal gene functions. Although advances in transformation efficiency and promoter usage have improved genetic studies, some basic steps in vector construction are still laborious and time-consuming. Gateway cloning technology solves this problem by increasing the efficiency of vector construction through the use of λ phage integrase proteins and att recombination sites. We developed a series of Gateway-compatible vectors for use in genetic studies in a range of fungal species. They contain nutritional and drug-resistance markers and can be utilized to manipulate different filamentous fungal genomes.

Characterization of a 5-azacytidine-induced developmental Aspergillus fumigatus variant.

The hypomethylating agent 5-azacytidine (5AC) is widely used in patients at risk of invasive mycoses. We sought to determine whether 5AC affects the developmental competence and virulence of Aspergillus fumigatus. Incubation of A. fumigatus strain 293 with 5AC induced high-frequency conversion to a fluffy-variant (Af293 (FL) ). The conidiation defect was bypassed by exposing Af293 (FL) to light during the initial 18 hours of growth on solid media. Transcriptional profiling revealed differential expression of multiple genes involved in G-protein signaling, including a putative G-protein coupled photoreceptor (opsin), suggesting that impaired signaling through a light-responsive pathway upstream of brlA is responsible for this phenotype. Af293 (FL) was fully virulent in fruit fly and murine models of invasive aspergillosis. Moreover, Af293 (FL) overexpressed aspergillopepsin F, had increased elastase activity and was more angioinvasive than the parental wild-type strain. The 5AC-induced A. fumigatus fluffy variant illustrates the potential effects of chemotherapeutic agents on the developmental and pathobiologic characteristics of opportunistic fungi.

Exploring the concordance of Aspergillus fumigatus pathogenicity in mice and Toll-deficient flies.

The pathogenicity of six mutants of Aspergillus fumigatus that had been previously characterized in mice was assessed in Toll-deficient Drosophila melanogaster flies. Four out of six mutants of A. fumigatus, which displayed attenuated virulence in mice due to defects in siderophore biosynthesis (DeltasidA, DeltasidD), PABA metabolism (H515), and starvation stress response (DeltacpcA), also had attenuated virulence in the fly model. In addition, similarly to previous findings in the mouse model, DeltasidG mutant that is defective in extracellular siderophore biosynthesis retained full virulence in Toll-deficient flies. Overall, our studies reveal a high level of concordance between fly and murine models of invasive aspergillosis.

Protostadienol biosynthesis and metabolism in the pathogenic fungus Aspergillus fumigatus.

Details of the fungal biosynthetic pathway to helvolic acid and other fusidane antibiotics remain obscure. During product characterization of oxidosqualene cyclases in Aspergillus fumigatus, we found the long-sought cyclase that makes (17Z)-protosta-17(20),24-dien-3beta-ol, the precursor of helvolic acid. We then identified a gene cluster encoding the pathway to helvolic acid, which is controlled by a transcription regulator (LaeA) associated with fungal virulence. Evidence regarding the evolutionary origin and taxonomic distribution of fusidane biosynthesis is also presented.

A new Mycobacterium species causing diffuse lepromatous leprosy.

Mycobacterium leprae causes leprosy. M leprae strains collected worldwide have been genetically clonal, which poorly explains the varying severity and clinical features of the disease. We discovered a new Mycobacterium species from 2 patients who died of diffuse lepromatous leprosy (DLL). The Mycobacterium was purified from heavily infected, freshly frozen autopsy liver tissue followed by DNA extraction in 1 case. Paraffin-embedded skin tissue was used for DNA extraction in another case. Six genes of the organism were amplified by polymerase chain reaction, sequenced on cloning or from amplicons, and analyzed. Significant genetic differences with M leprae were found, including a 2.1% divergence of the 16S ribosomal RNA (rRNA) gene, a highly conserved marker of bacterial evolution, and 6% to 14% mismatches among 5 less conserved genes. Phylogenetic analyses of the genes of 16S rRNA, rpoB, and hsp65 indicated that the 2 most related organisms evolved from a common ancestor that had branched from other mycobacteria. These results and the unique clinicopathologic features of DLL led us to propose Mycobacterium lepromatosis sp nov. This species may account for some of the clinical and geographic variability of leprosy. This finding may have implications for the research and diagnosis of leprosy.

Caspofungin-mediated beta-glucan unmasking and enhancement of human polymorphonuclear neutrophil activity against Aspergillus and non-Aspergillus hyphae.

BACKGROUND: We investigated whether caspofungin and other echinocandins have immune-enhancing properties that influence human polymorphonuclear neutrophil (PMN)-mediated mold hyphal damage. MATERIALS AND METHODS: Using aniline blue staining, we compared patterns of beta-glucan exposure in Aspergillus fumigatus, Aspergillus terreus, Rhizopus oryzae, Fusarium solani, Fusarium oxysporum, Scedosporium prolificans, and Scedosporium apiospermum hyphae after caspofungin exposure. We also determined PMN-mediated hyphal damage occurring with or without preexposure to caspofungin or with preexposure to the combination of caspofungin and anti-beta-glucan monoclonal antibody, using 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-sH-tetrazolium hydroxide (XTT) assay. RESULTS: Preincubation with caspofungin (32 microg/mL for R. oryzae; 0.0625 microg/mL for other isolates) increased exposure to beta-glucan. PMN-induced damage increased after caspofungin exposure and was further augmented by the addition of anti-beta-glucan antibody. Preincubation with micafungin or anidulafungin had similar effects on PMN-induced damage of A. fumigatus hyphae. Finally, preexposure of A. fumigatus, but not S. prolificans, to caspofungin induced expression of Dectin-1 by PMN. CONCLUSIONS: The results of the present study suggest inducement of beta-glucan unmasking by echinocandins and enhancement of PMN activity against mold hyphae, thereby supporting the immunopharmacologic mode of action of echinocandins.

Chemosensitization of fungal pathogens to antimicrobial agents using benzo analogs.

Activities of conventional antifungal agents, fludioxonil, strobilurin and antimycin A, which target the oxidative and osmotic stress response systems, were elevated by coapplication of certain benzo analogs (aldehydes and acids). Fungal tolerance to 2,3-dihydroxybenzaldehyde or 2,3-dihydroxybenzoic acid was found to rely upon mitochondrial superoxide dismutase (SOD2) or glutathione reductase (GLR1), genes regulated by the HOG1 signaling pathway, respectively. Thus, certain benzo analogs can be effective at targeting cellular oxidative stress response systems. The ability of these compounds to chemosensitize fungi for improved control with conventional antifungal agents is discussed.

Gliotoxin production in Aspergillus fumigatus contributes to host-specific differences in virulence.

BACKGROUND: Gliotoxin is a epipolythiodioxopiperazine toxin that is made by the filamentous fungus Aspergillus fumigatus. Gliotoxin has a wide range of effects on metazoan cells in culture, including induction of apoptosis through inhibition of Nf-kappaB, and inhibition of superoxide production by phagocytes. These activities have led to the proposal that gliotoxin contributes to pathogenesis during invasive aspergillosis. We tested this hypothesis by creating isogenic strains of gliotoxin-producing and nonproducing strains. METHODS: We deleted gliP, the gene that encodes the nonribosomal peptide synthetase GliP. GliP catalyzes the first biosynthetic step in the synthesis of gliotoxin. We then tested for gliotoxin production and virulence in different animal models. RESULTS: Deletion of gliP resulted in strains that were wild type for growth, but they did not synthesize gliotoxin. Transformation of gliP deletion mutants with a full copy of gliP restored gliotoxin production. The gliP deletion strain had attenuated virulence in nonneutropenic mice immunosuppressed with corticosteroids, but had normal virulence in neutropenic mice. It also had reduced virulence in a Drosophila melanogaster model. CONCLUSIONS: Gliotoxin only contributes to the virulence of A. fumigatus in nonneutropenic mice and in fruit flies with functional phagocytes. These results suggest that the principal targets of gliotoxin are neutrophils or other phagocytes.

Fungal genomics: a tool to explore central metabolism of Aspergillus fumigatus and its role in virulence.

Aspergillus fumigatus is an opportunistic pathogenic fungus that primarily infects neutropenic animal hosts. This fungus is found throughout the world, can utilize a wide range of substrates for carbon and nitrogen sources, and is capable of growing at elevated temperatures. The ability to grow at high temperatures and utilize a range of nutrient substrates for growth potentially contributes to this being the number one human pathogenic mold worldwide. The recently completed genome sequence for this fungus creates an opportunity to examine how central metabolic pathways and their regulation contribute to pathogenesis. A review of the existing literature illustrates that genes involved in the biosynthesis of key nutrients are essential for pathogenesis in A. fumigatus. In addition, nutrient sensing and regulation of biosynthetic pathways also contribute to fungal pathogenesis. The advent of improved methods for manipulating the genome of A. fumigatus, along with the completed genome sequence, now make it feasible to investigate the role of all metabolic pathways and control of these pathways in fungal virulence.

Enhancement of fludioxonil fungicidal activity by disrupting cellular glutathione homeostasis with 2,5-dihydroxybenzoic acid.

The activity of fludioxonil, a phenylpyrrole fungicide, is elevated by coapplication of the aspirin/salicylic acid metabolite, 2,5-dihydroxybenzoic acid (2,5-DHBA). Fludioxonil activity is potentiated through a mitogen-activated protein kinase (MAPK) pathway that regulates osmotic/oxidative stress-responses. 2,5-DHBA disrupts cellular GSH (reduced glutathione)/GSSG (oxidized glutathione) homeostasis, further stressing the oxidative stress-response system. This stress enhances fludioxonil activity. 2,5-DHBA treatment also prevents tolerance of MAPK mutants resistant to fludioxonil.

Novel mitogen-activated protein kinase MpkC of Aspergillus fumigatus is required for utilization of polyalcohol sugars.

The genome of Aspergillus fumigatus has four genes that encode mitogen-activated protein kinases (MAPKs), sakA/hogA, mpkA, mpkB, and mpkC. The functions of the MpkB and MpkC MAPKs are unknown for A. fumigatus and the closely related and genetically amenable species Aspergillus nidulans. mpkC deletion mutants of A. fumigatus were made and their phenotypes characterized. The mpkC deletion mutants were viable and had normal conidial germination and hyphal growth on minimal or complete media. This is in contrast to deletion mutants with deletions in the closely related MAPK gene sakA/hogA that we previously reported had a nitrogen source-dependent germination phenotype. Similarly, the growth of the mpkC deletion mutants was wild type on high-osmolarity medium. Consistent with these two MAP kinase genes regulating different cellular responses, we determined that the mpkC deletion mutants were unable to grow on minimal medium with sorbitol or mannitol as the sole carbon source. This result implicates MpkC signaling in carbon source utilization. Changes in mRNA levels for sakA and mpkC were measured in response to hypertonic stress, oxidative stress, and a shift from glucose to sorbitol to determine if there was overlap in the SakA and MpkC signaling pathways. These studies demonstrated that SakA- and MpkC-dependent patterns of change in mRNA levels are distinct and have minimal overlap in response to these environmental stresses.

Toll-deficient Drosophila flies as a fast, high-throughput model for the study of antifungal drug efficacy against invasive aspergillosis and Aspergillus virulence.

Invasive aspergillosis (IA) is the most important opportunistic mycosis in immunosuppressed patients. The lack of a sufficient number of effective antifungals and our incomplete understanding of the pathogenesis of IA contribute to its overall unfavorable prognosis. Studies of drug efficacy against IA and Aspergillus virulence rely on conventional animal models that are laborious and use limited numbers of animals; alternative, less cumbersome in vivo models are desirable. Using different inoculation models of IA, we found that Toll-deficient Drosophila flies exposed to voriconazole (VRC), the preferred drug for the treatment of IA in humans, had significantly better survival rates and lower tissue fungal burdens than did those not exposed to VRC. Furthermore, Toll-deficient Drosophila flies infected with an alb1-deleted hypovirulent Aspergillus mutant had significantly better survival rates than did those infected with a wild-type Aspergillus strain. Therefore, the Drosophila fly is a fast, high-throughput in vivo model for the study of drug efficacy against IA and Aspergillus virulence.

Cholesterol import by Aspergillus fumigatus and its influence on antifungal potency of sterol biosynthesis inhibitors.

High mortality rates from invasive aspergillosis in immunocompromised patients are prompting research toward improved antifungal therapy and better understanding of fungal physiology. Herein we show that Aspergillus fumigatus, the major pathogen in aspergillosis, imports exogenous cholesterol under aerobic conditions and thus compromises the antifungal potency of sterol biosynthesis inhibitors. Adding serum to RPMI medium led to enhanced growth of A. fumigatus and extensive import of cholesterol, most of which was stored as ester. Growth enhancement and sterol import also occurred when the medium was supplemented with purified cholesterol instead of serum. Cells cultured in RPMI medium with the sterol biosynthesis inhibitors itraconazole or voriconazole showed retarded growth, a dose-dependent decrease in ergosterol levels, and accumulation of aberrant sterol intermediates. Adding serum or cholesterol to the medium partially rescued the cells from the drug-induced growth inhibition. We conclude that cholesterol import attenuates the potency of sterol biosynthesis inhibitors, perhaps in part by providing a substitute for membrane ergosterol. Our findings establish significant differences in sterol homeostasis between filamentous fungi and yeast. These differences indicate the potential value of screening aspergillosis antifungal agents in serum or other cholesterol-containing medium. Our results also suggest an explanation for the antagonism between itraconazole and amphotericin B, the potential use of Aspergillus as a model for sterol trafficking, and new insights for antifungal drug development.

Aspergillus hyphae in infected tissue: evidence of physiologic adaptation and effect on culture recovery.

Microbiologic cultures of fungi are routinely incubated at ambient temperatures in room air, and the rate of recovery of Aspergillus species from clinical specimens is poor. Failure of current culture methods to mimic the physiologic temperature and low-oxygen environment found in hypha-laden infected tissue may underlie this poor recovery. Experiments were performed to compare the recovery of Aspergillus spp. incubated at 35 degrees C in 6% O(2)-10% CO(2) with that at 25 degrees C in room air. The samples tested included Aspergillus-infected tissue specimens from a dog model and human autopsies, experimental anaerobically stressed Aspergillus inocula, and 10,062 consecutive clinical specimens. Culture at 35 degrees C in 6% O(2)-10% CO(2) significantly enhanced the recovery of Aspergillus spp. from the infected autopsy tissue samples. Incubation at 35 degrees C alone resulted in approximately 10-fold-improved culture recovery from the experimentally stressed hyphae, and the 6% O(2)-10% CO(2) atmosphere independently favored growth under temperature-matched conditions. Finally, incubation at 35 degrees C (in room air) improved the overall recovery of Aspergillus spp. from clinical specimens by 31%. Culture at 35 degrees C in a microaerobic atmosphere significantly enhances the recovery of Aspergillus spp. from various sources. Aspergillus hyphae growing in infected tissue appear to be adapted to the physiologic temperature and hypoxic milieu.

[Cloning of the Aspergillus fumigatus squalene epoxidase gene].

OBJECTIVE: To clone Aspergillus fumigatus squalene epoxidase gene and to further investigate its role in terbinafine resistance. METHODS: The A.fumigatus genomic DNA library was transformed into pyrG-A. fumigatus strain protoplasts with polyethylene glycol-mediated transformation protocol. TRB-resistant pyrG+ transformants were then isolated by being plated on MM-U with TRB (0.625 mg/L) plates. After confirmation of terbinafine-resistance by using both disk diffusion and NCCLS M38-A microdilution antifungal susceptibility testing, the gene conferring terbinafine-resistance was identified. Finally, the gene was cloned and retransformed into pyrG-A. fumigatus strain. RESULTS: From a total of 5x10(4) transformants, one TRB-resistant pyrG+ transformant was isolated, which showed the terbinafine-specific resistance without cross-resistance to any other antifungals. A. fumigatus squalene epoxidase gene was further identified to confer this terbinafine-resistance. As a result, the complete A. fumigatus squalene epoxidase gene was firstly cloned. Finally, the transformants with extra copies of A. fumigatus squalene epoxidase gene, again, showed the specific resistance to terbinafine. CONCLUSION: Extra copies of A. fumigatus squalene epoxidase gene, which was cloned for the first time in this study, could result in A. fumigatus resistance to terbinafine. This is a novel mechanism of terbinafine-resistance that needs further investigation for its clinical significance.

Isogenic auxotrophic mutant strains in the Aspergillus fumigatus genome reference strain AF293.

Aspergillus fumigatus is a ubiquitous fungus that is a frequent opportunistic pathogen in immunosuppressed patients. Because of its role as a pathogen, it is of considerable experimental interest. A set of auxotrophic isogenic strains in the A. fumigatus genome reference strain AF293 has been developed. Using molecular genetic methods, arginine and lysine auxotrophs were made by deletion of argB and lysB, respectively. Transformation of these auxotrophic strains with plasmids carrying argB or lysB, respectively, results in efficient integration at these loci. Finally, these strains are able to form stable diploids, which should further facilitate analysis of gene functions in this fungus. Furthermore, the development of this isogenic set of auxotrophic strains in the AF293 background will enable investigators to study this important opportunistic human pathogen with greater facility.

Extra copies of the Aspergillus fumigatus squalene epoxidase gene confer resistance to terbinafine: genetic approach to studying gene dose-dependent resistance to antifungals in A. fumigatus.

With the increasing use of antifungals such as amphotericin B, itraconazole, voriconazole, caspofungin, and terbinafine (TRB) in patients at high risk for invasive aspergillosis, resistance of Aspergillus fumigatus to these agents will ultimately emerge. Due to the limited availability of molecular genetics for A. fumigatus, few studies have addressed its mechanisms of resistance to antifungals. We transformed A. fumigatus protoplasts with a pyrG-based A. fumigatus genomic DNA library (constructed in the multicopy nonintegrating vector pRG3-AMA1-NotI, which also has the pyr-4 gene for selection). We obtained one pyrG(+) transformant that grew in medium containing a fungicidal concentration (0.625 microg/ml) of TRB. To determine whether TRB resistance in that transformant was plasmid dependent, we evicted the plasmid and found concomitant loss of uracil prototrophy and TRB resistance. DNA sequence analysis identified the gene responsible for TRB resistance as the A. fumigatus squalene epoxidase gene (ERG1), which encodes the target enzyme of TRB. Authentic A. fumigatus ERG1, amplified from the genome and cloned into pRG3-AMA1-NotI, also conferred TRB-specific resistance. This molecular approach has the potential to enhance our knowledge of the mechanisms of A. fumigatus resistance to modern antifungals.

A mitogen-activated protein kinase that senses nitrogen regulates conidial germination and growth in Aspergillus fumigatus.

We show that the mitogen-activated protein (MAP) kinase pathway that responds to osmotic stress in Aspergillus fumigatus is also involved in nutritional sensing. This MAP kinase regulates conidial germination in response to the nitrogen source and is activated upon starvation for either carbon or nitrogen during vegetative growth.