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Phytotoxin production in Aspergillus terreus is regulated by independent environmental signals.

Gressler M, Meyer F, Heine D, Hortschansky P, Hertweck C, Brock M - Elife (2015)

Bottom Line: Here, signals, mediators, and biological effects of terrein production were studied in the fungus Aspergillus terreus to elucidate the contribution of terrein to ecological competition.Terrein causes fruit surface lesions and inhibits plant seed germination.Independent signal transduction allows complex sensing of the environment and, combined with its broad spectrum of biological activities, terrein provides a prominent example of adapted secondary metabolite production in response to environmental competition.

View Article: PubMed Central - PubMed

Affiliation: Microbial Biochemistry and Physiology, Leibniz Institute for Natural Product Research and Infection Biology, Hans Knoell Institute, Jena, Germany.

ABSTRACT
Secondary metabolites have a great potential as pharmaceuticals, but there are only a few examples where regulation of gene cluster expression has been correlated with ecological and physiological relevance for the producer. Here, signals, mediators, and biological effects of terrein production were studied in the fungus Aspergillus terreus to elucidate the contribution of terrein to ecological competition. Terrein causes fruit surface lesions and inhibits plant seed germination. Additionally, terrein is moderately antifungal and reduces ferric iron, thereby supporting growth of A. terreus under iron starvation. In accordance, the lack of nitrogen or iron or elevated methionine levels induced terrein production and was dependent on either the nitrogen response regulators AreA and AtfA or the iron response regulator HapX. Independent signal transduction allows complex sensing of the environment and, combined with its broad spectrum of biological activities, terrein provides a prominent example of adapted secondary metabolite production in response to environmental competition.

No MeSH data available.


Related in: MedlinePlus

High performance liquid chromatography (HPLC) analysis of extracts from Aspergillus terreus strains after cultivation in fruit juices and from infected nectarines and apples.(A–D) HPLC analyses of culture extracts from fruit juices after inoculation with SBUG844_PterA:lacZ (blue line) and mock-inoculated juices that served as negative controls (green line). Culture supernatants were extracted 48 hr post inoculation: (A) carrot juice, (B) banana juice, (C) apple juice, (D) peach juice. 1 = terrein. (E, F) HPLC analyses of fruit extracts after infection with A. terreus wild-type SBUG844ΔakuB (blue line) and terrein biosynthesis gene cluster mutants ΔterA (red) and ΔterR (violet). Mock-infected fruits served as negative controls (green line): (E) nectarine, (F) apple. 1 = terrein.DOI:http://dx.doi.org/10.7554/eLife.07861.004
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fig1s1: High performance liquid chromatography (HPLC) analysis of extracts from Aspergillus terreus strains after cultivation in fruit juices and from infected nectarines and apples.(A–D) HPLC analyses of culture extracts from fruit juices after inoculation with SBUG844_PterA:lacZ (blue line) and mock-inoculated juices that served as negative controls (green line). Culture supernatants were extracted 48 hr post inoculation: (A) carrot juice, (B) banana juice, (C) apple juice, (D) peach juice. 1 = terrein. (E, F) HPLC analyses of fruit extracts after infection with A. terreus wild-type SBUG844ΔakuB (blue line) and terrein biosynthesis gene cluster mutants ΔterA (red) and ΔterR (violet). Mock-infected fruits served as negative controls (green line): (E) nectarine, (F) apple. 1 = terrein.DOI:http://dx.doi.org/10.7554/eLife.07861.004

Mentions: In agreement with a lack of terrein production, β-galactosidase activity was near the detection limit when the A. terreus PterA:lacZ strain was grown on glucose minimal medium. In contrast, and in agreement with previous observations, a 200–500 fold induction was observed on PDB medium (Figure 1A). Similarly, on Sabouraud and yeast extract-peptone-dextrose (YPD) medium, induction levels reached 10–30% compared with PDB. However, potato broth or casamino acids did not induce the cluster without the addition of glucose, indicating that glucose appears to be required for terrein production rather than repressing gene cluster induction as shown for other SM gene clusters (Theilgaard et al., 1997; Brakhage et al., 2004; Gressler et al., 2011). Indeed, when glucose medium was supplemented with 1% casamino acids as the nitrogen source, a 20–30 fold activation was detected. Since terrein can cause lesions on fruit surfaces and inhibits plant seed germination (Kamata et al., 1983; Zaehle et al., 2014), we assumed that sugar-rich fruit and root juices might have a strong stimulatory capacity. Therefore, we cultivated the reporter strain on banana, carrot, peach, and apple juice. β-Galactosidase activities from these media exceeded the activity of the already strong inducing PDB medium (Figure 1B) by a factor of at least five. Additionally, in subsequent LC analyses of culture extracts, a distinct ultraviolet signal for terrein was detected (Figure 1—figure supplement 1A–D). This led us to infect fresh bananas with the A. terreus ΔakuB strain (the parental strain for gene deletions; Gressler et al., 2011), a ΔterR mutant lacking the transcriptional activator, and a ΔterA deletion mutant that lacks the key polyketide synthase from the cluster.10.7554/eLife.07861.003Figure 1.Terrein production and expression of terA on plant-derived media.


Phytotoxin production in Aspergillus terreus is regulated by independent environmental signals.

Gressler M, Meyer F, Heine D, Hortschansky P, Hertweck C, Brock M - Elife (2015)

High performance liquid chromatography (HPLC) analysis of extracts from Aspergillus terreus strains after cultivation in fruit juices and from infected nectarines and apples.(A–D) HPLC analyses of culture extracts from fruit juices after inoculation with SBUG844_PterA:lacZ (blue line) and mock-inoculated juices that served as negative controls (green line). Culture supernatants were extracted 48 hr post inoculation: (A) carrot juice, (B) banana juice, (C) apple juice, (D) peach juice. 1 = terrein. (E, F) HPLC analyses of fruit extracts after infection with A. terreus wild-type SBUG844ΔakuB (blue line) and terrein biosynthesis gene cluster mutants ΔterA (red) and ΔterR (violet). Mock-infected fruits served as negative controls (green line): (E) nectarine, (F) apple. 1 = terrein.DOI:http://dx.doi.org/10.7554/eLife.07861.004
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Related In: Results  -  Collection

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fig1s1: High performance liquid chromatography (HPLC) analysis of extracts from Aspergillus terreus strains after cultivation in fruit juices and from infected nectarines and apples.(A–D) HPLC analyses of culture extracts from fruit juices after inoculation with SBUG844_PterA:lacZ (blue line) and mock-inoculated juices that served as negative controls (green line). Culture supernatants were extracted 48 hr post inoculation: (A) carrot juice, (B) banana juice, (C) apple juice, (D) peach juice. 1 = terrein. (E, F) HPLC analyses of fruit extracts after infection with A. terreus wild-type SBUG844ΔakuB (blue line) and terrein biosynthesis gene cluster mutants ΔterA (red) and ΔterR (violet). Mock-infected fruits served as negative controls (green line): (E) nectarine, (F) apple. 1 = terrein.DOI:http://dx.doi.org/10.7554/eLife.07861.004
Mentions: In agreement with a lack of terrein production, β-galactosidase activity was near the detection limit when the A. terreus PterA:lacZ strain was grown on glucose minimal medium. In contrast, and in agreement with previous observations, a 200–500 fold induction was observed on PDB medium (Figure 1A). Similarly, on Sabouraud and yeast extract-peptone-dextrose (YPD) medium, induction levels reached 10–30% compared with PDB. However, potato broth or casamino acids did not induce the cluster without the addition of glucose, indicating that glucose appears to be required for terrein production rather than repressing gene cluster induction as shown for other SM gene clusters (Theilgaard et al., 1997; Brakhage et al., 2004; Gressler et al., 2011). Indeed, when glucose medium was supplemented with 1% casamino acids as the nitrogen source, a 20–30 fold activation was detected. Since terrein can cause lesions on fruit surfaces and inhibits plant seed germination (Kamata et al., 1983; Zaehle et al., 2014), we assumed that sugar-rich fruit and root juices might have a strong stimulatory capacity. Therefore, we cultivated the reporter strain on banana, carrot, peach, and apple juice. β-Galactosidase activities from these media exceeded the activity of the already strong inducing PDB medium (Figure 1B) by a factor of at least five. Additionally, in subsequent LC analyses of culture extracts, a distinct ultraviolet signal for terrein was detected (Figure 1—figure supplement 1A–D). This led us to infect fresh bananas with the A. terreus ΔakuB strain (the parental strain for gene deletions; Gressler et al., 2011), a ΔterR mutant lacking the transcriptional activator, and a ΔterA deletion mutant that lacks the key polyketide synthase from the cluster.10.7554/eLife.07861.003Figure 1.Terrein production and expression of terA on plant-derived media.

Bottom Line: Here, signals, mediators, and biological effects of terrein production were studied in the fungus Aspergillus terreus to elucidate the contribution of terrein to ecological competition.Terrein causes fruit surface lesions and inhibits plant seed germination.Independent signal transduction allows complex sensing of the environment and, combined with its broad spectrum of biological activities, terrein provides a prominent example of adapted secondary metabolite production in response to environmental competition.

View Article: PubMed Central - PubMed

Affiliation: Microbial Biochemistry and Physiology, Leibniz Institute for Natural Product Research and Infection Biology, Hans Knoell Institute, Jena, Germany.

ABSTRACT
Secondary metabolites have a great potential as pharmaceuticals, but there are only a few examples where regulation of gene cluster expression has been correlated with ecological and physiological relevance for the producer. Here, signals, mediators, and biological effects of terrein production were studied in the fungus Aspergillus terreus to elucidate the contribution of terrein to ecological competition. Terrein causes fruit surface lesions and inhibits plant seed germination. Additionally, terrein is moderately antifungal and reduces ferric iron, thereby supporting growth of A. terreus under iron starvation. In accordance, the lack of nitrogen or iron or elevated methionine levels induced terrein production and was dependent on either the nitrogen response regulators AreA and AtfA or the iron response regulator HapX. Independent signal transduction allows complex sensing of the environment and, combined with its broad spectrum of biological activities, terrein provides a prominent example of adapted secondary metabolite production in response to environmental competition.

No MeSH data available.


Related in: MedlinePlus