Mitochondrial function in the yeast form of the pathogenic fungus Paracoccidioides brasiliensis

Carbon and Nitrogen Sources Have No Impact on the Organization and Composition of Ustilago maydis Respiratory Supercomplexes

Respiratory supercomplexes are found in mitochondria of eukaryotic cells and some bacteria. A hypothetical role of these supercomplexes is electron channeling, which in principle should increase the respiratory chain efficiency and ATP synthesis. In addition to the four classic respiratory complexes and the ATP synthase, U. maydis mitochondria contain three type II NADH dehydrogenases (NADH for reduced nicotinamide adenine dinucleotide) and the alternative oxidase. Changes in the composition of the respiratory supercomplexes due to energy requirements have been reported in certain organisms. In this study, we addressed the organization of the mitochondrial respiratory complexes in U. maydis under diverse energy conditions. Supercomplexes were obtained by solubilization of U. maydis mitochondria with digitonin and separated by blue native polyacrylamide gel electrophoresis (BN-PAGE). The molecular mass of supercomplexes and their probable stoichiometries were 1200 kDa (I₁:IV₁), 1400 kDa (I₁:III₂), 1600 kDa (I₁:III₂:IV₁), and 1800 kDa (I₁:III₂:IV₂). Concerning the ATP synthase, approximately half of the protein is present as a dimer and half as a monomer. The distribution of respiratory supercomplexes was the same in all growth conditions. We did not find evidence for the association of complex II and the alternative NADH dehydrogenases with other respiratory complexes.

Updates and Comparative Analysis of the Mitochondrial Genomes of Paracoccidioides spp. Using Oxford Nanopore MinION Sequencing

The mitochondrial genome of the Paracoccidioides brasiliensis reference isolate Pb18 was first sequenced and described by Cardoso et al. (2007), as a circular genome with a size of 71.3 kb and containing 14 protein coding genes, 25 tRNAs, and the large and small subunits of ribosomal RNA. Later in 2011, Desjardins et al. (2011) obtained partial assemblies of mitochondrial genomes of P. lutzii (Pb01), P. americana (Pb03), and P. brasiliensis sensu stricto (Pb18), although with a size of only 43.1 kb for Pb18. Sequencing errors or other limitations resulting from earlier technologies, and the advantages of NGS (short and long reads), prompted us to improve and update the mtDNA sequences and annotations of two Paracoccidioides species. Using Oxford Nanopore and Illumina read sequencing, we generated high-quality complete de novo mitochondrial genome assemblies and annotations for P. brasiliensis (Pb18) and P. americana (Pb03). Both assemblies were characterized by an unusually long spacer or intron region (>50 kb) between exons 2 and 3 of the nad5 gene, which was moderately conserved between Pb03 and Pb18 but not similar to other reported sequences, except for an unassigned contig in the 2011 assembly of Pb03. The reliability of the insert missing from previous mtDNA genome assemblies was confirmed by inspection of the individual Nanopore read sequences containing nad5 coding DNA, and experimentally by PCR for Pb18. We propose that the insert may aid replication initiation and may be excised to produce a smaller structural variant. The updated mtDNA genomes should enable more accurate SNP and other comparative or evolutionary analyses and primer/probe designs. A comparative analysis of the mtDNA from 32 isolates of Paracoccidioides spp., using the SNPs of the aligned mitochondrial genomes, showed groupings within the brasiliensis species complex that were largely consistent with previous findings from only five mitochondrial loci.

Heterologous expression of mitochondrial nicotinamide adenine dinucleotide transporter (Ndt1) from Aspergillus fumigatus rescues impaired growth in Δndt1Δndt2 Saccharomyces cerevisiae strain

Our understanding of nicotinamide adenine dinucleotide mitochondrial transporter 1 (Ndt1A) in Aspergillus fumigatus remains poor. Thus, we investigated whether Ndt1A could alter fungi survival. To this end, we engineered the expression of an Ndt1A-encoding region in a Δndt1Δndt2 yeast strain. The resulting cloned Ndt1A protein promoted the mitochondrial uptake of nicotinamide adenine dinucleotide (NAD⁺), generating a large mitochondrial membrane potential. The NAD⁺ carrier utilized the electrochemical proton gradient to drive NAD⁺ entrance into mitochondria when the mitochondrial membrane potential was sustained by succinate. Its uptake has no impact on oxidative stress, and Ndt1A expression improved growth and survival of the Δndt1Δndt2 Saccharomyces cerevisiae strain.

Paracoccidioides Spp.: Virulence Factors and Immune-Evasion Strategies

Paracoccidioides spp. are dimorphic fungal pathogens responsible for one of the most relevant systemic mycoses in Latin America, paracoccidioidomycosis (PCM). Their exact ecological niche remains unknown; however, they have been isolated from soil samples and armadillos (Dasypus novemcinctus), which have been proposed as animal reservoir for these fungi. Human infection occurs by inhalation of conidia or mycelia fragments and is mostly associated with immunocompetent hosts inhabiting and/or working in endemic rural areas. In this review focusing on the pathogen perspective, we will discuss some of the microbial attributes and molecular mechanisms that enable Paracoccidioides spp. to tolerate, adapt, and ultimately avoid the host immune response, establishing infection.

Alternative oxidase mediates pathogen resistance in Paracoccidioides brasiliensis infection

BACKGROUND

Paracoccidioides brasiliensis is a human thermal dimorphic pathogenic fungus. Survival of P. brasiliensis inside the host depends on the adaptation of this fungal pathogen to different conditions, namely oxidative stress imposed by immune cells.

AIMS AND METHODOLOGY

In this study, we evaluated the role of alternative oxidase (AOX), an enzyme involved in the intracellular redox balancing, during host-P. brasiliensis interaction. We generated a mitotically stable P. brasiliensis AOX (PbAOX) antisense RNA (aRNA) strain with a 70% reduction in gene expression. We evaluated the relevance of PbAOX during interaction of conidia and yeast cells with IFN-γ activated alveolar macrophages and in a mouse model of infection. Additionally, we determined the fungal cell's viability and PbAOX in the presence of H₂O₂.

RESULTS

Interaction with IFN-γ activated alveolar macrophages induced higher levels of PbAOX gene expression in PbWt conidia than PbWt yeast cells. PbAOX-aRNA conidia and yeast cells had decreased viability after interaction with macrophages. Moreover, in a mouse model of infection, we showed that absence of wild-type levels of PbAOX in P. brasiliensis results in a reduced fungal burden in lungs at weeks 8 and 24 post-challenge and an increased survival rate. In the presence of H₂O₂, we observed that PbWt yeast cells increased PbAOX expression and presented a higher viability in comparison with PbAOX-aRNA yeast cells.

CONCLUSIONS

These data further support the hypothesis that PbAOX is important in the fungal defense against oxidative stress imposed by immune cells and is relevant in the virulence of P. brasiliensis.

Classical and alternative components of the mitochondrial respiratory chain in pathogenic fungi as potential therapeutic targets

The frequency of opportunistic fungal infection has increased drastically, mainly in patients who are immunocompromised due to organ transplant, leukemia or HIV infection. In spite of this, only a few classes of drugs with a limited array of targets, are available for antifungal therapy. Therefore, more specific and less toxic drugs with new molecular targets is desirable for the treatment of fungal infections. In this context, searching for differences between mitochondrial mammalian hosts and fungi in the classical and alternative components of the mitochondrial respiratory chain may provide new potential therapeutic targets for this purpose.

Involvement of an alternative oxidase in oxidative stress and mycelium-to-yeast differentiation in Paracoccidioides brasiliensis

Paracoccidioides brasiliensis is a thermodimorphic human pathogenic fungus that causes paracoccidioidomycosis (PCM), which is the most prevalent systemic mycosis in Latin America. Differentiation from the mycelial to the yeast form (M-to-Y) is an essential step for the establishment of PCM. We evaluated the involvement of mitochondria and intracellular oxidative stress in M-to-Y differentiation. M-to-Y transition was delayed by the inhibition of mitochondrial complexes III and IV or alternative oxidase (AOX) and was blocked by the association of AOX with complex III or IV inhibitors. The expression of P. brasiliensis aox (Pbaox) was developmentally regulated through M-to-Y differentiation, wherein the highest levels were achieved in the first 24 h and during the yeast exponential growth phase; Pbaox was upregulated by oxidative stress. Pbaox was cloned, and its heterologous expression conferred cyanide-resistant respiration in Saccharomyces cerevisiae and Escherichia coli and reduced oxidative stress in S. cerevisiae cells. These results reinforce the role of PbAOX in intracellular redox balancing and demonstrate its involvement, as well as that of other components of the mitochondrial respiratory chain complexes, in the early stages of the M-to-Y differentiation of P. brasiliensis.

Experimental medical mycological research in Latin America - a 2000-2009 overview

An overview of current trends in Latin American Experimental Medical Mycological research since the beginning of the 21(st) century is done (search from January 2000 to December 2009). Using the PubMed and LILACS databases, the authors have chosen publications on medically important fungi which, according to our opinion, are the most relevant because of their novelty, interest, and international impact, based on research made entirely in the Latin American region or as part of collaborative efforts with laboratories elsewhere. In this way, the following areas are discussed: 1) molecular identification of fungal pathogens; 2) molecular and clinical epidemiology on fungal pathogens of prevalence in the region; 3) cell biology; 4) transcriptome, genome, molecular taxonomy and phylogeny; 5) immunology; 6) vaccines; 7) new and experimental antifungals.