Quantitative Monitoring of Mycelial Growth of Aspergillus fumigatus in Liquid Culture by Optical Density

The Utilization of Bacillus subtilis to Design Environmentally Friendly Living Paints with Anti-Mold Properties

The anti-fungal properties of the probiotic bacterium Bacillus subtilis have been studied extensively in agriculture and ecology, but their applications in the built environment remain to be determined. Our work aims to utilize this biological component to introduce new diverse anti-mold properties into paint. "Mold" refers to the ubiquitous fungal species that generate visible multicellular filaments commonly found in household dust. The development of mold leads to severe health problems for occupants, including allergic response, hypersensitivity pneumonitis, and asthma, which have significant economic and clinical outcomes. We here demonstrate the robust effect of a commercial paint enhanced with Bacillus subtilis cells against the common mold agent, Aspergillus niger, and identify three biosynthetic clusters essential for this effect. Our results lay the foundation for bio-convergence and synthetic biology approaches to introduce renewable and environmentally friendly bio-anti-fungal agents into the built environment.

Real-time monitoring of mycelial growth in liquid culture using hyphal dispersion mutant of Aspergillus fumigatus

Hyphal pellet formation by Aspergillus species in liquid cultures is one of the main obstacles to high-throughput anti-Aspergillus reagent screening. We previously constructed a hyphal dispersion mutant of Aspergillus fumigatus by disrupting the genes encoding the primary cell wall α-1,3-glucan synthase Ags1 and putative galactosaminogalactan synthase Gtb3 (Δags1Δgtb3). Mycelial growth of the mutant in liquid cultures monitored by optical density was reproducible, and the dose-response of hyphal growth to antifungal agents has been quantified by optical density. However, Δags1Δgtb3 still forms hyphal pellets in some rich growth media. Here, we constructed a disruptant lacking all three α-1,3-glucan synthases and galactosaminogalactan synthase (Δags1Δags2Δags3Δgtb3), and confirmed that its hyphae were dispersed in all the media tested. We established an automatic method to monitor hyphal growth of the mutant in a 24-well plate shaken with a real-time plate reader. Dose-dependent growth suppression and unique growth responses to antifungal agents (voriconazole, amphotericin B, and micafungin) were clearly observed. A 96-well plate was also found to be useful for the evaluation of mycelial growth by optical density. Our method is potentially applicable to high-throughput screening for anti-Aspergillus agents.

Distinct transcriptional responses to fludioxonil in Aspergillus fumigatus and its ΔtcsC and Δskn7 mutants reveal a crucial role for Skn7 in the cell wall reorganizations triggered by this antifungal

BACKGROUND

Aspergillus fumigatus is a major fungal pathogen that causes severe problems due to its increasing resistance to many therapeutic agents. Fludioxonil is a compound that triggers a lethal activation of the fungal-specific High Osmolarity Glycerol pathway. Its pronounced antifungal activity against A. fumigatus and other pathogenic molds renders this agent an attractive lead substance for the development of new therapeutics. The group III hydride histidine kinase TcsC and its downstream target Skn7 are key elements of the multistep phosphorelay that represents the initial section of the High Osmolarity Glycerol pathway. Loss of tcsC results in resistance to fludioxonil, whereas a Δskn7 mutant is partially, but not completely resistant.

RESULTS

In this study, we compared the fludioxonil-induced transcriptional responses in the ΔtcsC and Δskn7 mutant and their parental A. fumigatus strain. The number of differentially expressed genes correlates well with the susceptibility level of the individual strains. The wild type and, to a lesser extend also the Δskn7 mutant, showed a multi-faceted stress response involving genes linked to ribosomal and peroxisomal function, iron homeostasis and oxidative stress. A marked difference between the sensitive wild type and the largely resistant Δskn7 mutant was evident for many cell wall-related genes and in particular those involved in the biosynthesis of chitin. Biochemical data corroborate this differential gene expression that does not occur in response to hyperosmotic stress.

CONCLUSIONS

Our data reveal that fludioxonil induces a strong and TcsC-dependent stress that affects many aspects of the cellular machinery. The data also demonstrate a link between Skn7 and the cell wall reorganizations that foster the characteristic ballooning and the subsequent lysis of fludioxonil-treated cells.

A New Benzaldehyde Derivative Exhibits Antiaflatoxigenic Activity against Aspergillus flavus

Aflatoxin B1 (AFB1) is the most potent naturally occurring carcinogen for humans and animals produced by the common fungus Aspergillus flavus (A. flavus). Aflatoxin (AF) contamination in commodities is a global concern related to the safety of food and feed, and it also impacts the agricultural economy. In this study, we investigated the AFB1-inhibiting activity of a new benzaldehyde derivative, 2-[(2-methylpyridin-3-yl)oxy]benzaldehyde (MPOBA), on A. flavus. It was found that MPOBA inhibited the production of AFB1 by A. flavus, with an IC50 value of 0.55 mM. Moreover, the inhibition of conidiation was also observed at the same concentration. The addition of MPOBA resulted in decreased transcript levels of the aflR gene, which encodes a key regulatory protein for the biosynthesis of AF, and also decreased transcript levels of the global regulator genes veA and laeA. These results suggested that MPOBA has an effect on the regulatory mechanism of the development and differentiation of conidia, leading to the inhibition of AFB1 production. In addition, the cytotoxicity study showed that MPOBA had a very low cytotoxic effect on the Madin-Darby canine kidney (MDCK) cell line. Therefore, MPOBA may be a potential compound for developing practically effective agents to control AF contamination.

Assessing thermal adaptation of a global sample of Aspergillus fumigatus: Implications for climate change effects

Aspergillus fumigatus is a common environmental mold and a major cause of opportunistic infections in humans. It's distributed among many ecological niches across the globe. A major virulence factor of A. fumigatus is its ability to grow at high temperature. However, at present, little is known about variations among strains in their growth at different temperatures and how their geographic origins may impact such variations. In this study, we analyzed 89 strains from 12 countries (Cameroon, Canada, China, Costa Rica, France, India, Iceland, Ireland, New Zealand, Peru, Saudi Arabia, and USA) representing diverse geographic locations and temperature environments. Each strain was grown at four temperatures and genotyped at nine microsatellite loci. Our analyses revealed a range of growth profiles, with significant variations among strains within individual geographic populations in their growths across the temperatures. No statistically significant association was observed between strain genotypes and their thermal growth profiles. Similarly geographic separation contributed little to differences in thermal adaptations among strains and populations. The combined analyses among genotypes and growth rates at different temperatures in the global sample suggest that most natural populations of A. fumigatus are capable of rapid adaptation to temperature changes. We discuss the implications of our results to the evolution and epidemiology of A. fumigatus under increasing climate change.

Online Biomass Monitoring Enables Characterization of the Growth Pattern of Aspergillus fumigatus in Liquid Shake Conditions

Numerous filamentous fungal species are extensively studied due to their role as model organisms, workhorses in biotechnology, or as pathogens for plants, animals, and humans. Growth studies are mainly carried out on solid media. However, studies concerning gene expression, biochemistry, or metabolism are carried out usually in liquid shake conditions, which do not correspond to the growth pattern on solid media. The reason for this practice is the problem of on-line growth monitoring of filamentous fungal species, which usually form pellets in liquid shake cultures. Here, we compared the time-consuming and tedious process of dry-weight determination of the mold Aspergillus fumigatus with online monitoring of biomass in liquid shake culture by the parallelizable CGQ (“cell growth quantifier”), which implements dynamic biomass determination by backscattered light measurement. The results revealed a strong correlation of CGQ-mediated growth monitoring and classical biomass measurement of A. fumigatus grown over a time course. Moreover, CGQ-mediated growth monitoring displayed the difference in growth of A. fumigatus in response to the limitation of iron or nitrogen as well as the growth defects of previously reported mutant strains (ΔhapX, ΔsrbA). Furthermore, the frequently used wild-type strain Af293 showed largely decreased and delayed growth in liquid shake cultures compared to other strains (AfS77, A1160p+, AfS35). Taken together, the CGQ allows for robust, automated biomass monitoring of A. fumigatus during liquid shake conditions, which largely facilitates the characterization of the growth pattern of filamentous fungal species.

A Novel Monoclonal Antibody 1D2 That Broadly Inhibits Clinically Important Aspergillus Species

Aspergillus fumigatus is a ubiquitous airborne fungus, is the predominant cause (>90%) of invasive aspergillosis (IA) in immunosuppressed patients and has a high mortality. New approaches to prevention and treatment are needed because of the poor efficacy, toxicity and side effects of the current anti-Aspergillus drugs on patients. Thus, we aim to explore a new avenue to combat Aspergillus infection by using a novel monoclonal antibody (mAb) 1D2 against a glycoprotein on the cell wall of Aspergillus. The ability of this mAb to inhibit attachment, germination, and growth of Aspergillus conidia and hyphae in vitro were examined. A dose-dependent growth inhibition of Aspergillus conidia in the presence of mAb 1D2 was found. The mAb 1D2 inhibited attachment of Aspergillus conidia to an untreated slide surface and fibronectin-treated surface compared to an unrelated mAb 6B10. When conidia were exposed to 1D2 concomitantly with inoculation into culture media, the mAb prevented the swelling and germination of conidia. This inhibitory ability of 1D2 was less apparent if it was added two hours after inoculation. Damage to hyphae was also observed when 1D2 was added to Aspergillus hyphae that had been incubated in media overnight. These in vitro results indicate that mAb 1D2 broadly inhibits clinically important Aspergillus species and has a promising therapeutic effect both as prophylaxis to inhibit an Aspergillus infection as well as a treatment.

Cell Wall Integrity and Its Industrial Applications in Filamentous Fungi

Signal transduction pathways regulating cell wall integrity (CWI) in filamentous fungi have been studied taking into account findings in budding yeast, and much knowledge has been accumulated in recent years. Given that the cell wall is essential for viability in fungi, its architecture has been analyzed in relation to virulence, especially in filamentous fungal pathogens of plants and humans. Although research on CWI signaling in individual fungal species has progressed, an integrated understanding of CWI signaling in diverse fungi has not yet been achieved. For example, the variety of sensor proteins and their functional differences among different fungal species have been described, but the understanding of their general and species-specific biological functions is limited. Our long-term research interest is CWI signaling in filamentous fungi. Here, we outline CWI signaling in these fungi, from sensor proteins required for the recognition of environmental changes to the regulation of cell wall polysaccharide synthesis genes. We discuss the similarities and differences between the functions of CWI signaling factors in filamentous fungi and in budding yeast. We also describe the latest findings on industrial applications, including those derived from studies on CWI signaling: the development of antifungal agents and the development of highly productive strains of filamentous fungi with modified cell surface characteristics by controlling cell wall biogenesis.