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Regulation of sulphur assimilation is essential for virulence and affects iron homeostasis of the human-pathogenic mould Aspergillus fumigatus.

Amich J, Schafferer L, Haas H, Krappmann S - PLoS Pathog. (2013)

Bottom Line: Surprisingly, A. fumigatus is able to utilize volatile sulphur compounds produced by its methionine catabolism, a process that has not been described before and that is MetR-dependent.The A. fumigatus MetR transcriptional activator is important for virulence in both leukopenic mice and an alternative mini-host model of aspergillosis, as it was essential for the development of pulmonary aspergillosis and supported the systemic dissemination of the fungus.Taken together, this study provides evidence that regulation of sulphur assimilation is not only crucial for A. fumigatus virulence but also affects the balance of iron in this prime opportunistic pathogen.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Infectious Diseases, Julius-Maximilians-University Würzburg, Würzburg, Germany.

ABSTRACT
Sulphur is an essential element that all pathogens have to absorb from their surroundings in order to grow inside their infected host. Despite its importance, the relevance of sulphur assimilation in fungal virulence is largely unexplored. Here we report a role of the bZIP transcription factor MetR in sulphur assimilation and virulence of the human pathogen Aspergillus fumigatus. The MetR regulator is essential for growth on a variety of sulphur sources; remarkably, it is fundamental for assimilation of inorganic S-sources but dispensable for utilization of methionine. Accordingly, it strongly supports expression of genes directly related to inorganic sulphur assimilation but not of genes connected to methionine metabolism. On a broader scale, MetR orchestrates the comprehensive transcriptional adaptation to sulphur-starving conditions as demonstrated by digital gene expression analysis. Surprisingly, A. fumigatus is able to utilize volatile sulphur compounds produced by its methionine catabolism, a process that has not been described before and that is MetR-dependent. The A. fumigatus MetR transcriptional activator is important for virulence in both leukopenic mice and an alternative mini-host model of aspergillosis, as it was essential for the development of pulmonary aspergillosis and supported the systemic dissemination of the fungus. MetR action under sulphur-starving conditions is further required for proper iron regulation, which links regulation of sulphur metabolism to iron homeostasis and demonstrates an unprecedented regulatory crosstalk. Taken together, this study provides evidence that regulation of sulphur assimilation is not only crucial for A. fumigatus virulence but also affects the balance of iron in this prime opportunistic pathogen.

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Related in: MedlinePlus

Functional categories of genes regulated by MetR as deduced from RNA-seq data.Categorisation was performed via the FungiFun suite (https://sbi.hki-jena.de/FungiFun/FungiFun.cgi) to identify functional groups for genes that are less (A) and more abundantly (B) expressed in the metRΔ mutant AfS167 compared to its wild-type progenitor ATCC 46645 after eight hours of culture under sulphur-limiting conditions. The minor pie charts (left panels) indicate the percentage of genes with and without annotation in the GO database; the larger pie charts (right panels) represent the deduced functional groups of the annotated genes and indicate percentages of genes for each category.
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ppat-1003573-g006: Functional categories of genes regulated by MetR as deduced from RNA-seq data.Categorisation was performed via the FungiFun suite (https://sbi.hki-jena.de/FungiFun/FungiFun.cgi) to identify functional groups for genes that are less (A) and more abundantly (B) expressed in the metRΔ mutant AfS167 compared to its wild-type progenitor ATCC 46645 after eight hours of culture under sulphur-limiting conditions. The minor pie charts (left panels) indicate the percentage of genes with and without annotation in the GO database; the larger pie charts (right panels) represent the deduced functional groups of the annotated genes and indicate percentages of genes for each category.

Mentions: Following the observation that the expression of genes whose products are required for sulphur assimilation is regulated by MetR, we became interested in understanding to what extent any transcriptional remodeling that takes place under sulphur-limiting conditions is MetR-dependent. For this purpose, overnight-grown mycelia of the wild-type and metRΔ strains were shifted from cultures containing sufficient levels (5 mM) of methionine serving as sole S-source to media containing low methionine levels (0.2 mM) over a time frame of eight hours before RNA was harvested. Previous culturing experiments had shown that methionine depletion became manifest within this time frame, so this experimental set-up allows assessment of any MetR contribution to the transcriptional response upon mild S-depletion. Nucleic acid samples were prepared from two biological replicates each to perform digital transcriptome analyses by the RNA-seq approach (see Materials and Methods for details). Comparison of both transcriptomes under this specific condition revealed that 288 genes were downregulated and 349 were upregulated in the metRΔ strain with respect to its wild-type progenitor (>1.5-fold change, p-value<0.05) (Table 1 and Table S1). Categorisation via the FungiFun suite [55] revealed that the main cellular functions affected by the absence of MetR are membrane transport, metabolism, carbohydrate metabolism, and oxidation/reduction (Fig. 6). Therefore, MetR action is required for the correct remodeling of these processes to counteract conditions of sulphur depletion. To further understand this adaptation, we performed a deeper functional categorisation. Various genes assigned to cation homeostasis were less abundant in the metRΔ mutant (Table 2), suggesting a strong dysfunction in the regulation of the metabolism of these ions. In addition, several genes whose products participate in sugar, glucoside, polyol and carboxylate metabolism were downregulated what highlights the greatly different metabolic status of the mutant under sulphur starvation. Furthermore, genes related to cellular export and secretion were also identified, hinting a distinct interaction with the environment. Surprisingly, several genes related to mRNA synthesis and were also found to be downregulated, which indicates a interplay of MetR regulation with other transcription factors and cell cycle regulation.


Regulation of sulphur assimilation is essential for virulence and affects iron homeostasis of the human-pathogenic mould Aspergillus fumigatus.

Amich J, Schafferer L, Haas H, Krappmann S - PLoS Pathog. (2013)

Functional categories of genes regulated by MetR as deduced from RNA-seq data.Categorisation was performed via the FungiFun suite (https://sbi.hki-jena.de/FungiFun/FungiFun.cgi) to identify functional groups for genes that are less (A) and more abundantly (B) expressed in the metRΔ mutant AfS167 compared to its wild-type progenitor ATCC 46645 after eight hours of culture under sulphur-limiting conditions. The minor pie charts (left panels) indicate the percentage of genes with and without annotation in the GO database; the larger pie charts (right panels) represent the deduced functional groups of the annotated genes and indicate percentages of genes for each category.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3757043&req=5

ppat-1003573-g006: Functional categories of genes regulated by MetR as deduced from RNA-seq data.Categorisation was performed via the FungiFun suite (https://sbi.hki-jena.de/FungiFun/FungiFun.cgi) to identify functional groups for genes that are less (A) and more abundantly (B) expressed in the metRΔ mutant AfS167 compared to its wild-type progenitor ATCC 46645 after eight hours of culture under sulphur-limiting conditions. The minor pie charts (left panels) indicate the percentage of genes with and without annotation in the GO database; the larger pie charts (right panels) represent the deduced functional groups of the annotated genes and indicate percentages of genes for each category.
Mentions: Following the observation that the expression of genes whose products are required for sulphur assimilation is regulated by MetR, we became interested in understanding to what extent any transcriptional remodeling that takes place under sulphur-limiting conditions is MetR-dependent. For this purpose, overnight-grown mycelia of the wild-type and metRΔ strains were shifted from cultures containing sufficient levels (5 mM) of methionine serving as sole S-source to media containing low methionine levels (0.2 mM) over a time frame of eight hours before RNA was harvested. Previous culturing experiments had shown that methionine depletion became manifest within this time frame, so this experimental set-up allows assessment of any MetR contribution to the transcriptional response upon mild S-depletion. Nucleic acid samples were prepared from two biological replicates each to perform digital transcriptome analyses by the RNA-seq approach (see Materials and Methods for details). Comparison of both transcriptomes under this specific condition revealed that 288 genes were downregulated and 349 were upregulated in the metRΔ strain with respect to its wild-type progenitor (>1.5-fold change, p-value<0.05) (Table 1 and Table S1). Categorisation via the FungiFun suite [55] revealed that the main cellular functions affected by the absence of MetR are membrane transport, metabolism, carbohydrate metabolism, and oxidation/reduction (Fig. 6). Therefore, MetR action is required for the correct remodeling of these processes to counteract conditions of sulphur depletion. To further understand this adaptation, we performed a deeper functional categorisation. Various genes assigned to cation homeostasis were less abundant in the metRΔ mutant (Table 2), suggesting a strong dysfunction in the regulation of the metabolism of these ions. In addition, several genes whose products participate in sugar, glucoside, polyol and carboxylate metabolism were downregulated what highlights the greatly different metabolic status of the mutant under sulphur starvation. Furthermore, genes related to cellular export and secretion were also identified, hinting a distinct interaction with the environment. Surprisingly, several genes related to mRNA synthesis and were also found to be downregulated, which indicates a interplay of MetR regulation with other transcription factors and cell cycle regulation.

Bottom Line: Surprisingly, A. fumigatus is able to utilize volatile sulphur compounds produced by its methionine catabolism, a process that has not been described before and that is MetR-dependent.The A. fumigatus MetR transcriptional activator is important for virulence in both leukopenic mice and an alternative mini-host model of aspergillosis, as it was essential for the development of pulmonary aspergillosis and supported the systemic dissemination of the fungus.Taken together, this study provides evidence that regulation of sulphur assimilation is not only crucial for A. fumigatus virulence but also affects the balance of iron in this prime opportunistic pathogen.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Infectious Diseases, Julius-Maximilians-University Würzburg, Würzburg, Germany.

ABSTRACT
Sulphur is an essential element that all pathogens have to absorb from their surroundings in order to grow inside their infected host. Despite its importance, the relevance of sulphur assimilation in fungal virulence is largely unexplored. Here we report a role of the bZIP transcription factor MetR in sulphur assimilation and virulence of the human pathogen Aspergillus fumigatus. The MetR regulator is essential for growth on a variety of sulphur sources; remarkably, it is fundamental for assimilation of inorganic S-sources but dispensable for utilization of methionine. Accordingly, it strongly supports expression of genes directly related to inorganic sulphur assimilation but not of genes connected to methionine metabolism. On a broader scale, MetR orchestrates the comprehensive transcriptional adaptation to sulphur-starving conditions as demonstrated by digital gene expression analysis. Surprisingly, A. fumigatus is able to utilize volatile sulphur compounds produced by its methionine catabolism, a process that has not been described before and that is MetR-dependent. The A. fumigatus MetR transcriptional activator is important for virulence in both leukopenic mice and an alternative mini-host model of aspergillosis, as it was essential for the development of pulmonary aspergillosis and supported the systemic dissemination of the fungus. MetR action under sulphur-starving conditions is further required for proper iron regulation, which links regulation of sulphur metabolism to iron homeostasis and demonstrates an unprecedented regulatory crosstalk. Taken together, this study provides evidence that regulation of sulphur assimilation is not only crucial for A. fumigatus virulence but also affects the balance of iron in this prime opportunistic pathogen.

Show MeSH
Related in: MedlinePlus