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Invasive aspergillosis is a disease responsible for high mortality rates, caused mainly by Aspergillus fumigatus. The available drugs are limited and this disease continues to occur at an unacceptable frequency. Gene disruption is essential in the search for new drug targets. An efficient protocol for A. fumigatus gene disruption was described but it requires ethidium bromide, a genotoxic agent, for DNA staining. Therefore, the present study tested SYBR safe TM , a non-genotoxic DNA stain, in A. fumigatus gene disruption protocol. The chosen gene was cipC, which has already been disrupted successfully in our laboratory. A deletion cassette was constructed in Saccharomyces cerevisiae and used in A. fumigatus transformation. There was no statistical difference between the tested DNA stains. The success rate of S. cerevisiae transformation was 63.3% for ethidium bromide and 70% for SYBR safe TM . For A. fumigatus gene disruption, the success rate for ethidium bromide was 100 and 97% for SYBR safe TM . In conclusion, SYBR safe TM efficiently replaced ethidium bromide, making this dye a safe and efficient alternative for DNA staining in A. fumigatus gene disruption.

Aspergillus fumigatus is the main causative agent of invasive aspergillosis, a disease that affects immunocompromised patients and has a high mortality rate. We previously observed that the transcription of a cipC-like gene was increased when A. fumigatus encountered an increased CO 2 concentration, as occurs during the infection process. CipC is a protein of unknown function that might be associated with fungal pathogenicity. In this study, the cipC gene was disrupted in A. fumigatus to evaluate its importance for fungal pathogenicity. The gene was replaced, and the germination, growth phenotype, stress responses, and virulence of the resultant mutant were assessed. Although cipC was not essential, its deletion attenuated A. fumigatus virulence in a low-dose murine infection model, suggesting the involvement of the cipC gene in the virulence of this fungus. This study is the first to disrupt the cipC gene in A. fumigatus., (© 2017 APMIS. Published by John Wiley & Sons Ltd.)

Carbon dioxide (CO(2)) and its hydration product bicarbonate (HCO(3)(-)) are essential molecules in various physiological processes of all living organisms. The reversible interconversion between CO(2) and HCO(3)(-) is in equilibrium. This reaction is slow without catalyst, but can be rapidly facilitated by Zn(2+)-metalloenzymes named carbonic anhydrases (CAs). To gain an insight into the function of multiple clades of fungal CA, we chose to investigate the filamentous fungi Aspergillus fumigatus and A. nidulans. We identified four and two CAs in A. fumigatus and A. nidulans, respectively, named cafA-D and canA-B. The cafA and cafB genes are constitutively, strongly expressed whereas cafC and cafD genes are weakly expressed but CO(2)-inducible. Heterologous expression of the A. fumigatus cafB, and A. nidulans canA and canB genes completely rescued the high CO(2)-requiring phenotype of a Saccharomyces cerevisiae Deltance103 mutant. Only the DeltacafA DeltacafB and DeltacanB deletion mutants were unable to grow at 0.033% CO(2), of which growth defects can be restored by high CO(2). Defects in the CAs can affect Aspergilli conidiation. Furthermore, A. fumigatus DeltacafA, DeltacafB, DeltacafC, DeltacafD and DeltacafA DeltacafB mutant strains are fully virulent in a low-dose murine infection.

Background: Calcineurin, a serine/threonine-specific protein phosphatase, plays an important role in the control of cell morphology and virulence in fungi. Calcineurin regulates localization and activity of a transcription factor called CRZ1. Recently, we characterize Aspergillus fumigatus CRZ1 homologue, AfCrzA. Here, we investigate which pathways are influenced by A. fumigatus AfCrzA during a short pulse of calcium by comparatively determining the transcriptional profile of A. fumigatus wild type and DeltaAfcrzA mutant strains., Results: We were able to observe 3,622 genes modulated in at least one timepoint in the mutant when compared to the wild type strain (3,211 and 411 at 10 and 30 minutes, respectively). Decreased mRNA abundance in the DeltacrzA was seen for genes encoding calcium transporters, transcription factors and genes that could be directly or indirectly involved in calcium metabolism. Increased mRNA accumulation was observed for some genes encoding proteins involved in stress response. AfCrzA overexpression in A. fumigatus increases the expression of several of these genes. The deleted strain of one of these genes, AfRcnA, belonging to a class of endogenous calcineurin regulators, calcipressins, had more calcineurin activity after exposure to calcium and was less sensitive to menadione 30 microM, hydrogen peroxide 2.5 mM, EGTA 25 mM, and MnCl2 25 mM. We constructed deletion, overexpression, and GFP fusion protein for the closely related A. nidulans AnRcnA. GFP::RcnA was mostly detected along the germling, did not accumulate in the nuclei and its location is not affected by the cellular response to calcium chloride., Conclusion: We have performed a transcriptional profiling analysis of the A. fumigatus DeltaAfcrzA mutant strain exposed to calcium stress. This provided an excellent opportunity to identify genes and pathways that are under the influence of AfCrzA. AfRcnA, one of these selected genes, encodes a modulator of calcineurin activity. Concomitantly with A. fumigatus AfrcnA molecular analysis, we decided to exploit the conserved features of A. nidulans calcineurin system and investigated the A. nidulans AnRcnA homologue. A. nidulans AnRcnA mutation is suppressing CnaA mutation and it is responsible for modulating the calcineurin activity and mRNA accumulation of genes encoding calcium transporters.

Calcineurin plays an important role in the control of cell morphology and virulence in fungi. Calcineurin is a serine/threonine-specific protein phosphatase heterodimer consisting of a catalytic subunit A and a regulatory subunit B. A mutant of Aspergillus fumigatus lacking the calcineurin A (calA) catalytic subunit exhibited defective hyphal morphology related to apical extension and branching growth, which resulted in drastically decreased filamentation. Here, we investigated which pathways are influenced by A. fumigatus calcineurin during proliferation by comparatively determining the transcriptional profile of A. fumigatus wild type and DeltacalA mutant strains. Our results showed that the mitochondrial copy number is reduced in the DeltacalA mutant strain, and the mutant has increased alternative oxidase (aoxA) mRNA accumulation and activity. Furthermore, we identified four genes that encode transcription factors that have increased mRNA expression in the DeltacalA mutant. Deletion mutants for these transcription factors had reduced susceptibility to itraconazole, caspofungin, and sodium dodecyl sulfate (SDS).

Here, we characterize the Aspergillus fumigatus homologue ncsA Neuronal Calcium Sensor. We showed that ncsA is not an essential gene and ncsA growth was decreased in the presence of EGTA and SDS. Furthermore, the ncsA mutant is more resistant to calcium chloride. NcsA:mRFP localizes to the cytoplasm and its cellular localization is not affected by the cellular response to either calcium chloride or EGTA. The ncsA mutant strain is more sensitive to voriconazole, itraconazole, and amphotericin. Polar growth in the DeltancsA mutant was also considerably more affected by lovastatin than in the wild type strain. The Spitzenkörper can be visualized in both strains and although the vacuolar system does not seem to be very different, there is an increase in the staining intensity on the germling surface of the ncsA strain. NcsA promotes pmcA and pmcB expression and therefore there is a reduced expression of these ion pumps in the DeltancsA mutant background, and also of other genes involved in the response to calcium in A. fumigatus. The ncsA inactivation mutation is not causing loss of virulence in a low dose murine infection when compared to the corresponding wild type strain.

Phosphate is an ion that is essential for fungal growth. The systems for inorganic phosphate (P(i)) acquisition in eukaryotic cells (PHO) have been characterized as a low-affinity (that assures a supply of P(i) at normal or high external P(i) concentrations) and a high-affinity (activated in response to P(i) starvation). Here, as an initial step to understand the PHO pathway in Aspergillus fumigatus, we characterized the PHO80 homologue, PhoB(PHO80). We show that the DeltaphoB(PHO80) mutant has a polar growth defect (i.e., a delayed germ tube emergence) and, by phenotypic and phosphate uptake analyses, establish a link between PhoB(PHO80), calcineurin and calcium metabolism. Microarray hybridizations carried out with RNA obtained from wild-type and DeltaphoB(PHO80) mutant cells identify Afu4g03610 (phoD(PHO84)), Afu7g06350 (phoE(PHO89)), Afu4g06020 (phoC(PHO81)), and Afu2g09040 (vacuolar transporter Vtc4) as more expressed both in the DeltaphoB(PHO80) mutant background and under phosphate-limiting conditions of 0.1mM P(i). Epifluorescence microscopy revealed accumulation of poly-phosphate in DeltaphoB(PHO80) vacuoles, which was independent of extracellular phosphate concentration. Surprisingly, a phoD(PHO84) deletion mutant is indistinguishable phenotypically from the corresponding wild-type strain. mRNA analyses suggest that protein kinase A absence supports the expression of PHO genes in A. fumigatus. Furthermore, DeltaphoB(PHO80) and DeltaphoD(PHO84) mutant are fully virulent in a murine low dose model for invasive aspergillosis.

The protein phosphatase calcineurin is an important mediator connecting calcium-dependent signalling to various cellular responses in multiple organisms. In fungi calcineurin acts largely through regulating Crz1p-like transcription factors. Here we characterize an Aspergillus fumigatus CRZ1 homologue, CrzA and demonstrate its mediation of cellular tolerance to increased concentrations of calcium and manganese. In addition to acute sensitivity to these ions, and decreased conidiation, the crzA null mutant suffers altered expression of calcium transporter mRNAs under high concentrations of calcium, and loss of virulence when compared with the corresponding complemented and wild-type strains. We use multiple expression analyses to probe the transcriptional basis of A. fumigatus calcium tolerance identifying several genes having calA and/or crzA dependent mRNA accumulation patterns. We also demonstrate that contrary to previous findings, the gene encoding the Aspergillus nidulans calcineurin subunit homologue, cnaA, is not essential and that the cnaA deletion mutant shares the morphological phenotypes observed in the corresponding A. fumigatus mutant, DeltacalA. Exploiting the A. nidulans model system, we have linked calcineurin activity with asexual developmental induction, finding that CrzA supports appropriate developmental induction in a calcineurin and brlA-dependent manner in both species.

Aspergillus fumigatus is an aggressive opportunistic pathogen of humans as well as a major allergen. Environmental sensing and retrieving essential nutrients from the environment are general metabolic traits associated with the growth of this saprophytic fungus. Two important mediators of calcium signals in eukaryotic cells are the Ca(2+)-binding protein calmodulin and the Ca(2+)/calmodulin-dependent phosphatase calcineurin. Calcineurin is a heterodimer that consists of a catalytic subunit A and a Ca(2+)/calmodulin binding unit. We deleted the A. fumigatus calA gene, which encodes the calcineurin A catalytic subunit, and demonstrated that this gene is not essential in this fungus. The DeltacalA mutant strain has severe defects in growth extension, branching and conidial architecture. Furthermore, the A. fumigatus DeltacalA mutant strain has decreased fitness in a low dose murine infection and cannot grow in fetal bovine serum (FBS). After potassium phosphate was added to liquid FBS, the DeltacalA mutant strain could grow with the characteristic phenotype of the DeltacalA mutation. When A. fumigatus calcineurin is inhibited by tacrolimus in a phosphate depleted medium, there is a reduction in the inorganic phosphate transport and six putative phosphate transporter genes have altered mRNA levels. However, there is no effect on the acid phosphatase activity. These results suggest that calcineurin is involved in the regulation of the PHO pathway in A. fumigatus. Our work on calcineurin opens new venues for the research on sensing and nutrient acquisition in A. fumigatus.

For a comprehensive evaluation of genes that have their expression modulated during exposure of the mycelia to voriconazole, we performed a large-scale analysis of gene expression in Aspergillus fumigatus using a microarray hybridization approach. By comparing the expression of genes between the reference time and after addition of voriconazole (30, 60, 120, and 240 min), we identified 2,271 genes differentially expressed in the wild-type strain. To validate the expression of some of these genes during exposure to voriconazole, we analyzed 13 genes showing higher expression in the presence of voriconazole by real-time RT-PCR. Although the magnitudes of induction differed between the two experimental systems, in about 85% of the cases they were in good agreement with the microarray data. To our knowledge this is the first study of microarray hybridization analysis for a filamentous fungus exposed to an antifungal agent. In our study, we have observed: (i) a decreased mRNA expression of various ergosterol biosynthesis genes; (ii) increased mRNA levels of genes involved in a variety of cell functions, such as transporters, transcription factors, proteins involved in cell metabolism, and hypothetical proteins; and (iii) the involvement of the cyclic AMP-protein kinase signaling pathway in the increased mRNA expression of several of these genes.

To increase the frequency of homologous recombination, we inactivated the KU80 homologue in Aspergillus fumigatus (named akuB(KU80)). Homologous integration reached about 80% for both calcineurin A (calA) and polyketide synthase pksP (alb1) genes in the akuB(KU80) mutant to 3 and 5%, respectively, when using a wild-type A. fumigatus strain. Deletion of akuB(KU80) had no influence on pathogenicity in a low-dose murine infection model.

The continuous use of triazoles can result in the development of drug resistance. Azole-resistant clinical isolates, spontaneous and induced mutants of Aspergillus fumigatus have been documented. The azoles block the ergosterol biosynthesis pathway by inhibiting the enzyme 14-alpha-demethylase, product of the CYP51. Fungal azole resistance involves both amino acid changes in the target site that alter drug-target interactions and those that decrease net azole accumulation. The reduced intracellular accumulation has also been correlated with overexpression of multidrug resistance (MDR) efflux transporter genes of the ATP-binding cassette (ABC) and the major facilitator superfamily (MFS) classes. About 20 genes are involved in the A. fumigatus ergosterol biosynthesis pathway. There are several duplicated genes in this pathway. Interestingly, erg3 and erg11 showed two copies in A. fumigatus. In general, Aspergillus spp. have proportionally more MFS transporter encoding genes than Saccharomyces cerevisiae, S. pombe, and Neurospora crassa. The drug H+ (12 and 14 spanners) sub-families are also proportionally greater than in the other species. Although the numbers of ABC transporter encoding genes are comparable, again the Aspergillus spp. have more ABC transporters related to multidrug permease than the other fungal species.

We investigated the evolution of resistance to the antifungal drug itraconazole in replicate populations of Aspergillus fumigatus that were founded from a strain with a genotype of sensitivity to a single drug and then propagated under uniform conditions. For each population, conidia were serially transferred 10 times to agar medium either with or without itraconazole. After 10 transfers in medium supplemented with itraconazole, 10 itraconazole-resistant mutant strains were isolated from two populations. These mutant strains had different growth rates and different levels of itraconazole resistance. Analysis of the ergosterol contents of these mutants showed that they accumulate ergosterol when they are grown in the presence of itraconazole. The replacement of the CYP51A gene of the wild-type strain changed the susceptibility pattern of this strain to one of itraconazole resistance only when CYP51A genes with N22D and M220I mutations were used as selectable marker genes. Real-time quantitative reverse transcription-PCR was used to assess the levels of expression of the Afumdr1, Afumdr2, Afumdr3, Afumdr4, AtrF transporter, CYP51A, and CYP51B genes in these mutant strains. Most mutants showed either constitutive high-level expression or induction upon exposure of Afumdr3, Afumdr4, and AtrF to itraconazole. Our results suggest that overexpression of drug efflux pumps and/or selection of drug target site mutations are at least partially responsible for itraconazole resistance and could be considered mechanisms for the emergence of clinical resistance to this drug.