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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

Antifungal activity of terrein and potato dextrose broth (PDB) medium from Aspergillus terreus wild-type cultivations.(A) AMM-G100Gln10 containing no iron addition (−Fe) or 2 mM FeCl3 were supplemented with 0, 1, 10, or 20 mM terrein and inoculated with conidia of Aspergillus fumigatus wild-type ATCC46645. Plates were incubated for 84 hr at 37°C until photographed. Terrein inhibits growth of A. fumigatus independently of the available iron concentration. (B) Analysis of the effect of A. terreus inoculated PDB culture broth on growth of A. terreus, A. fumigatus, and Fusarium graminearum. The basal medium for A. terreus and A. fumigatus was AMM-G50 medium with nitrate as the nitrogen source, whereas the medium for F. graminearum was additionally supplemented with 0.2% potato broth (AMM-G50 + 0.2%PB). All plates were supplemented either with 150 µl of PDB ethyl acetate extract from a mock-inoculated culture (PDB extract) or inoculated with A. terreus SBUG844 and cultivated for 4 d at 30°C (PDB metabolite extract). Photographs were taken after 4 d of incubation at 30°C.DOI:http://dx.doi.org/10.7554/eLife.07861.030
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fig7s2: Antifungal activity of terrein and potato dextrose broth (PDB) medium from Aspergillus terreus wild-type cultivations.(A) AMM-G100Gln10 containing no iron addition (−Fe) or 2 mM FeCl3 were supplemented with 0, 1, 10, or 20 mM terrein and inoculated with conidia of Aspergillus fumigatus wild-type ATCC46645. Plates were incubated for 84 hr at 37°C until photographed. Terrein inhibits growth of A. fumigatus independently of the available iron concentration. (B) Analysis of the effect of A. terreus inoculated PDB culture broth on growth of A. terreus, A. fumigatus, and Fusarium graminearum. The basal medium for A. terreus and A. fumigatus was AMM-G50 medium with nitrate as the nitrogen source, whereas the medium for F. graminearum was additionally supplemented with 0.2% potato broth (AMM-G50 + 0.2%PB). All plates were supplemented either with 150 µl of PDB ethyl acetate extract from a mock-inoculated culture (PDB extract) or inoculated with A. terreus SBUG844 and cultivated for 4 d at 30°C (PDB metabolite extract). Photographs were taken after 4 d of incubation at 30°C.DOI:http://dx.doi.org/10.7554/eLife.07861.030

Mentions: In general, siderophore-based iron acquisition is highly efficient and assumed to be more important than the reductive iron assimilation pathway. In A. fumigatus, growth and virulence defects caused by the interruption of the reductive iron assimilation pathway are only observed when the siderophore-based system is also inactivated (Blatzer et al., 2011). Therefore, to elucidate a positive effect of terrein on iron acquisition, we deleted the sidA gene in A. terreus that encodes the L-ornithine-N5-monooxygenase, a key enzyme in hydroxamate siderophore biosynthesis. Coprogen production was confirmed in the wild-type and a complemented mutant, but was completely lacking from the ΔsidA mutant (Figure 7—figure supplement 1). When analysed for growth phenotypes on solid media, all complemented mutants and the ΔterA strain behaved like the wild-type (Figure 7A and Figure 7—figure supplement 1A). The hapX mutant showed a reduced growth rate without iron supplementation (Figure 7A), which is in agreement with reduced coprogen production as shown above (Figure 6A). However, severe iron limitation from the addition of the iron chelator bathophenanthroline sulfonate (BPS) completely repressed growth of the hapX mutant (Figure 7A). The ΔsidA mutant displayed the most severe phenotype: while ΔsidA showed normal growth with slightly reduced conidiation in the presence of high to moderate iron concentrations (100 or 20 µM FeCl3) (Figure 7A), growth was strongly retarded when the iron concentration was reduced to 2 µM FeCl3. No growth was observed even after prolonged incubation when iron was omitted (Figure 7A). These phenotypes were cured when purified coprogen was externally added (Figure 7—figure supplement 1B). Interestingly, growth of the ΔsidA strain was also partially restored in the presence of ascorbic acid and, although to a lesser extent, by the addition of terrein (Figure 7A). This result is supported by previous studies on an A. nidulans ΔsidA mutant which was able to grow under iron limitation in the presence of ascorbic acid (Eisendle et al., 2003). Unexpectedly, terrein supplementation inhibited growth of an A. fumigatus sidA mutant, which was also true for an A. fumigatus wild-type strain (Figure 7—figure supplement 2). Subsequent analyses showed that growth of the phytopathogen Fusarium graminearum was also inhibited by terrein-containing culture extracts from A. terreus (Figure 7—figure supplement 2), indicating some antifungal properties of terrein against environmental competitors.10.7554/eLife.07861.028Figure 7.Siderophore production in sidA mutants and growth-supporting effect of terrein under iron limitation.


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)

Antifungal activity of terrein and potato dextrose broth (PDB) medium from Aspergillus terreus wild-type cultivations.(A) AMM-G100Gln10 containing no iron addition (−Fe) or 2 mM FeCl3 were supplemented with 0, 1, 10, or 20 mM terrein and inoculated with conidia of Aspergillus fumigatus wild-type ATCC46645. Plates were incubated for 84 hr at 37°C until photographed. Terrein inhibits growth of A. fumigatus independently of the available iron concentration. (B) Analysis of the effect of A. terreus inoculated PDB culture broth on growth of A. terreus, A. fumigatus, and Fusarium graminearum. The basal medium for A. terreus and A. fumigatus was AMM-G50 medium with nitrate as the nitrogen source, whereas the medium for F. graminearum was additionally supplemented with 0.2% potato broth (AMM-G50 + 0.2%PB). All plates were supplemented either with 150 µl of PDB ethyl acetate extract from a mock-inoculated culture (PDB extract) or inoculated with A. terreus SBUG844 and cultivated for 4 d at 30°C (PDB metabolite extract). Photographs were taken after 4 d of incubation at 30°C.DOI:http://dx.doi.org/10.7554/eLife.07861.030
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fig7s2: Antifungal activity of terrein and potato dextrose broth (PDB) medium from Aspergillus terreus wild-type cultivations.(A) AMM-G100Gln10 containing no iron addition (−Fe) or 2 mM FeCl3 were supplemented with 0, 1, 10, or 20 mM terrein and inoculated with conidia of Aspergillus fumigatus wild-type ATCC46645. Plates were incubated for 84 hr at 37°C until photographed. Terrein inhibits growth of A. fumigatus independently of the available iron concentration. (B) Analysis of the effect of A. terreus inoculated PDB culture broth on growth of A. terreus, A. fumigatus, and Fusarium graminearum. The basal medium for A. terreus and A. fumigatus was AMM-G50 medium with nitrate as the nitrogen source, whereas the medium for F. graminearum was additionally supplemented with 0.2% potato broth (AMM-G50 + 0.2%PB). All plates were supplemented either with 150 µl of PDB ethyl acetate extract from a mock-inoculated culture (PDB extract) or inoculated with A. terreus SBUG844 and cultivated for 4 d at 30°C (PDB metabolite extract). Photographs were taken after 4 d of incubation at 30°C.DOI:http://dx.doi.org/10.7554/eLife.07861.030
Mentions: In general, siderophore-based iron acquisition is highly efficient and assumed to be more important than the reductive iron assimilation pathway. In A. fumigatus, growth and virulence defects caused by the interruption of the reductive iron assimilation pathway are only observed when the siderophore-based system is also inactivated (Blatzer et al., 2011). Therefore, to elucidate a positive effect of terrein on iron acquisition, we deleted the sidA gene in A. terreus that encodes the L-ornithine-N5-monooxygenase, a key enzyme in hydroxamate siderophore biosynthesis. Coprogen production was confirmed in the wild-type and a complemented mutant, but was completely lacking from the ΔsidA mutant (Figure 7—figure supplement 1). When analysed for growth phenotypes on solid media, all complemented mutants and the ΔterA strain behaved like the wild-type (Figure 7A and Figure 7—figure supplement 1A). The hapX mutant showed a reduced growth rate without iron supplementation (Figure 7A), which is in agreement with reduced coprogen production as shown above (Figure 6A). However, severe iron limitation from the addition of the iron chelator bathophenanthroline sulfonate (BPS) completely repressed growth of the hapX mutant (Figure 7A). The ΔsidA mutant displayed the most severe phenotype: while ΔsidA showed normal growth with slightly reduced conidiation in the presence of high to moderate iron concentrations (100 or 20 µM FeCl3) (Figure 7A), growth was strongly retarded when the iron concentration was reduced to 2 µM FeCl3. No growth was observed even after prolonged incubation when iron was omitted (Figure 7A). These phenotypes were cured when purified coprogen was externally added (Figure 7—figure supplement 1B). Interestingly, growth of the ΔsidA strain was also partially restored in the presence of ascorbic acid and, although to a lesser extent, by the addition of terrein (Figure 7A). This result is supported by previous studies on an A. nidulans ΔsidA mutant which was able to grow under iron limitation in the presence of ascorbic acid (Eisendle et al., 2003). Unexpectedly, terrein supplementation inhibited growth of an A. fumigatus sidA mutant, which was also true for an A. fumigatus wild-type strain (Figure 7—figure supplement 2). Subsequent analyses showed that growth of the phytopathogen Fusarium graminearum was also inhibited by terrein-containing culture extracts from A. terreus (Figure 7—figure supplement 2), indicating some antifungal properties of terrein against environmental competitors.10.7554/eLife.07861.028Figure 7.Siderophore production in sidA mutants and growth-supporting effect of terrein under iron limitation.

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