The Role of Zinc in Gliotoxin Biosynthesis of Aspergillus fumigatus

Abstract

Zinc performs diverse physiological functions, and virtually all living organisms require zinc as an essential trace element. To identify the detailed function of zinc in fungal pathogenicity, we carried out cDNA microarray analysis using the model system of Aspergillus fumigatus, a fungal pathogen. From microarray analysis, we found that the genes involved in gliotoxin biosynthesis were upregulated when zinc was depleted, and the microarray data were confirmed by northern blot analysis. In particular, zinc deficiency upregulated the expression of GliZ, which encodes a Zn2-Cys6 binuclear transcription factor that regulates the expression of the genes required for gliotoxin biosynthesis. The production of gliotoxin was decreased in a manner inversely proportional to the zinc concentration, and the same result was investigated in the absence of ZafA, which is a zinc-dependent transcription activator. Interestingly, we found two conserved ZafA-binding motifs, 5′-CAAGGT-3′, in the upstream region of GliZ on the genome and discovered that deletion of the ZafA-binding motifs resulted in loss of ZafA-binding activity; gliotoxin production was decreased dramatically, as demonstrated with a GliZ deletion mutant. Furthermore, mutation of the ZafA-binding motifs resulted in an increase in the conidial killing activity of human macrophage and neutrophil cells, and virulence was decreased in a murine model. Finally, transcriptomic analysis revealed that the expression of ZafA and GliZ was upregulated during phagocytosis by macrophages. Taken together, these results suggest that zinc plays an important role in the pathogenicity of A. fumigatus by regulating gliotoxin production during the phagocytosis pathway to overcome the host defense system.

Zinc, an unexpected integrator of metabolism?

“…Yet, its singularity has been virtually overlooked [see however studies such as (Bütof et al , 2019)]. Unexpectedly, it was recently observed that the Aspergillus fumigatus mycotoxin, gliotoxin, had a function specifically involving zinc (Seo et al , 2019), and, because this metabolite could act as a specific zinc chelator, this opens up approaches to investigate in depth the role of zinc.…”

The Role of Zinc in Copper Homeostasis of Aspergillus fumigatus

“…By reducing the free zinc ion concentration inside neutrophils, a host can inhibit the growth of pathogens, and pathogens must look for other ways to survive. Our previous report showed that upregulation of gliotoxin production by zinc deprivation occurs in neutrophils [ 55 ]. In addition, upregulation of the metabolism of other metals is induced by zinc deprivation.…”

Nitrogen, Iron, and Zinc Acquisition: Key Nutrients to Aspergillus fumigatus Virulence

“…Evidence of this interconnection has been established in Fusarium fusjikuroi, since TOR controls—partially through AreA—the bikaverin biosynthetic genes [ 113 ]. Moreover, A. fumigatus produces more gliotoxin in Zn-limiting conditions than in Zn sufficiency and, surprisingly, Δ zafA is unable to produce gliotoxin [ 98 ]. The regulatory mechanism of gliotoxin biosynthesis by zinc has recently been described and matches what happens during infection.…”

“…The regulatory mechanism of gliotoxin biosynthesis by zinc has recently been described and matches what happens during infection. The low concentration of Zn upregulates the zafA gene, which, in addition to upregulating Zn-metabolism genes, upregulates expression of the gliotoxin biosynthetic cluster through GliZ activation [ 98 ]. The association between a low concentration of Zn and this toxin could be a response to overcome the nutritional and innate immunity of the host, since gliotoxin protects against phagocytosis [ 114 ] and Zn depletion is a common mechanism of host defense.…”