Aspergillus fumigatus versus Genus Aspergillus: Conservation, Adaptive Evolution and Specific Virulence Genes

NmrB (AN9181) expression is activated under oxidative stress conditions acting as a metabolic repressor of Aspergillus nidulans

Aspergilli comprise a diversity of species that have been extensively studied due to their catabolic diversity, biotechnological and ecological value, and pathogenicity. An impressive level of structural and functional conservation has been shown for aspergilli, regardless of many (yet) cryptic genomic elements. We have hypothesized the existence of conserved genes responsive to stress in aspergilli. To test the hypothesis of such conserved stress regulators in aspergilli, a straightforward computational strategy integrating well-established bioinformatic tools was used as the starting point. Specifically, five transcriptome-based datasets on exposure to organic compounds were used, covering three distinct Aspergillus species. Among the identified up-regulated genes, only one gene showed the same response in all conditions, AN9181. This gene encodes a protein containing a phenylcoumaran benzylic ether reductase-like domain and a Nitrogen metabolite repressor regulator domain (NmrA). Deletion of this gene caused significant phenotypic alterations compared to that of the parental strain across diverse conditions. Specifically, the deletion of AN9181 raised the mutant's metabolic activity in different nitrogen sources. The acquired data supports that AN9181 acts by repressing (slowing down) A. nidulans growth when exposed to aromatic compounds in a concentration dependent manner. The same phenotype was observed for amphotericin B. Finally, AN9181 underwent differential upregulation under oxidative stress conditions. Collectively, the data suggest that AN9181, herein assigned as NmrB (Nitrogen Metabolite Repression Regulator B), builds up the genetic machinery of perception of oxidative stress by negatively regulating growth under such conditions.

Immunoproteomics enable broad identification of new Aspergillus fumigatus antigens in severe equine asthma

Introduction

Severe equine asthma (SEA) is a common chronic disease of adult horses with characteristic recurrent airway obstruction and similarities to neutrophilic asthma in humans. As an extrinsic stimulus, hay dust exposure is a major risk factor and induces acute exacerbation in susceptible horses. However, single inducing agents of SEA have hardly been identified on a molecular basis. Aspergillus fumigatus (A. fumigatus) is a common mold species in hay and has been described as a major provoking agent of SEA.

Methods

Aiming to identify disease-relevant antigens, we analyzed A. fumigatus using an immunoproteomics approach on two-dimensional immunoblots of A. fumigatus protein probed with serum from environmentally matched asthmatic and healthy horses (n=5 pairs). A. fumigatus binding serum immunoglobulins (Pan-Ig), and the isotypes IgG4/7 and IgG3/5 were quantified for each protein spot and then compared between asthmatic and healthy horses.

Results and discussion

For 21 out of 289 spots serum immunoglobulin (Ig) binding was different between the two groups for Pan-Ig or the isotypes. If differences were detected, Pan-Ig and IgG4/7 binding to the proteins were lower, while IgG3/5 binding was higher in asthmatic than healthy horse sera. Proteins were extracted from the 21 spots of interest and analyzed by liquid chromatography mass spectrometry. Eight prioritized proteins (candidate antigens) were expressed as recombinant proteins. Some of these have been previously described as major or minor A. fumigatus allergens, alongside other proteins, most with hydrolase activity. Recombinant candidate antigens were tested on 1D immunoblots to confirm their relevance as antigens by serum antibody binding. Four proteins (beta-hexosaminidase, class II aldolase/adducin domain protein, glucoamylase, peptide hydrolase B0XX53) showed different antibody binding characteristics between asthmatic and healthy horses and are likely relevant antigens in SEA. Their identification can provide the basis for innovative diagnostics, prevention, or therapeutic approaches. Additionally, a more profound understanding of SEA and its potential underlying mechanisms can be established. Elevated serum IgG3/5 antibodies correlate with T helper cell 2 responses in other equine pathologies, and the recombinant SEA antigens developed here can become instrumental in analyzing the involvement of SEA-specific T cell responses and Ig responses in future studies.

Selection on plastic adherence leads to hyper-multicellular strains and incidental virulence in the budding yeast

Many disease-causing microbes are not obligate pathogens; rather, they are environmental microbes taking advantage of an ecological opportunity. The existence of microbes whose life cycle does not require a host and are not normally pathogenic, yet are well-suited to host exploitation, is an evolutionary puzzle. One hypothesis posits that selection in the environment may favor traits that incidentally lead to pathogenicity and virulence, or serve as pre-adaptations for survival in a host. An example of such a trait is surface adherence. To experimentally test the idea of 'accidental virulence', replicate populations of Saccharomyces cerevisiae were evolved to attach to a plastic bead for hundreds of generations. Along with plastic adherence, two multicellular phenotypes- biofilm formation and flor formation- increased; another phenotype, pseudohyphal growth, responded to the nutrient limitation. Thus, experimental selection led to the evolution of highly-adherent, hyper-multicellular strains. Wax moth larvae injected with evolved hyper-multicellular strains were significantly more likely to die than those injected with evolved non-multicellular strains. Hence, selection on plastic adherence incidentally led to the evolution of enhanced multicellularity and increased virulence. Our results support the idea that selection for a trait beneficial in the open environment can inadvertently generate opportunistic, 'accidental' pathogens.