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Aspergillus flavus grown in peptone as the carbon source exhibits spore density- and peptone concentration-dependent aflatoxin biosynthesis.

Yan S, Liang Y, Zhang J, Liu CM - BMC Microbiol. (2012)

Bottom Line: Metabolomic studies revealed that, in addition to inhibited AF biosynthesis, mycelia grown in peptone media with a high initial spore density showed suppressed fatty acid biosynthesis, reduced tricarboxylic acid (TCA) cycle intermediates, and increased pentose phosphate pathway products.Additions of TCA cycle intermediates had no effect on AF biosynthesis, suggesting the inhibited AF biosynthesis was not caused by depleted TCA cycle intermediates.This switching ability may offer Aspergillus species a competition advantage in natural ecosystems, producing AFs only when self-population is low and food is scarce.

View Article: PubMed Central - HTML - PubMed

Affiliation: Practaculture College, Gansu Agricultural University, Lanzhou 730070, China.

ABSTRACT

Background: Aflatoxins (AFs) are highly carcinogenic compounds produced by Aspergillus species in seeds with high lipid and protein contents. It has been known for over 30 years that peptone is not conducive for AF productions, although reasons for this remain unknown.

Results: In this study, we showed that when Aspergillus flavus was grown in peptone-containing media, higher initial spore densities inhibited AF biosynthesis, but promoted mycelial growth; while in glucose-containing media, more AFs were produced when initial spore densities were increased. This phenomenon was also observed in other AF-producing strains including A. parasiticus and A. nomius. Higher peptone concentrations led to inhibited AF production, even in culture with a low spore density. High peptone concentrations did however promote mycelial growth. Spent medium experiments showed that the inhibited AF production in peptone media was regulated in a cell-autonomous manner. mRNA expression analyses showed that both regulatory and AF biosynthesis genes were repressed in mycelia cultured with high initial spore densities. Metabolomic studies revealed that, in addition to inhibited AF biosynthesis, mycelia grown in peptone media with a high initial spore density showed suppressed fatty acid biosynthesis, reduced tricarboxylic acid (TCA) cycle intermediates, and increased pentose phosphate pathway products. Additions of TCA cycle intermediates had no effect on AF biosynthesis, suggesting the inhibited AF biosynthesis was not caused by depleted TCA cycle intermediates.

Conclusions: We here demonstrate that Aspergillus species grown in media with peptone as the sole carbon source are able to sense their own population densities and peptone concentrations to switch between rapid growth and AF production. This switching ability may offer Aspergillus species a competition advantage in natural ecosystems, producing AFs only when self-population is low and food is scarce.

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Additions of TCA cycle intermediates can not restore the AF biosynthesis in high initial spore density cultures. In A. flavus A3.2890 mycelia grown in PMS media initiated with 104 and 106 spores/ml, 0.5 mM or 5 mM TCA cycle intermediates, fumaric acid, malic acid and succinic acid, were added at the beginning of the culture. AFs were extracted from media and analyzed by TLC after 3-day cultivations.
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Figure 7: Additions of TCA cycle intermediates can not restore the AF biosynthesis in high initial spore density cultures. In A. flavus A3.2890 mycelia grown in PMS media initiated with 104 and 106 spores/ml, 0.5 mM or 5 mM TCA cycle intermediates, fumaric acid, malic acid and succinic acid, were added at the beginning of the culture. AFs were extracted from media and analyzed by TLC after 3-day cultivations.

Mentions: To test if reduced TCA cycle intermediates in mycelia are the primary cause of reduced AF biosynthesis in the high initial spore density culture, malic acid, fumaric acid and succinic acid were added to the PMS medium at the concentrations of 0.5 mM or 5 mM, and 0.5 or 5 mM NaCl was added to the culture as a control, and then performed liquid incubation with the final spore densities of 104 or 106 per ml using freshly prepared A. flavus A3.2890 spore suspensions. TLC analyses were performed for AFs extracted from the media. We observed that none of these treatments had any significant effect on AF production. No AF production was observed in any of the high initial spore density cultures (Figure 7). These results suggest that the inhibited AF biosynthesis in high initial spore density cultures was unlikely caused by reduced levels of TCA cycle intermediates.


Aspergillus flavus grown in peptone as the carbon source exhibits spore density- and peptone concentration-dependent aflatoxin biosynthesis.

Yan S, Liang Y, Zhang J, Liu CM - BMC Microbiol. (2012)

Additions of TCA cycle intermediates can not restore the AF biosynthesis in high initial spore density cultures. In A. flavus A3.2890 mycelia grown in PMS media initiated with 104 and 106 spores/ml, 0.5 mM or 5 mM TCA cycle intermediates, fumaric acid, malic acid and succinic acid, were added at the beginning of the culture. AFs were extracted from media and analyzed by TLC after 3-day cultivations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3412747&req=5

Figure 7: Additions of TCA cycle intermediates can not restore the AF biosynthesis in high initial spore density cultures. In A. flavus A3.2890 mycelia grown in PMS media initiated with 104 and 106 spores/ml, 0.5 mM or 5 mM TCA cycle intermediates, fumaric acid, malic acid and succinic acid, were added at the beginning of the culture. AFs were extracted from media and analyzed by TLC after 3-day cultivations.
Mentions: To test if reduced TCA cycle intermediates in mycelia are the primary cause of reduced AF biosynthesis in the high initial spore density culture, malic acid, fumaric acid and succinic acid were added to the PMS medium at the concentrations of 0.5 mM or 5 mM, and 0.5 or 5 mM NaCl was added to the culture as a control, and then performed liquid incubation with the final spore densities of 104 or 106 per ml using freshly prepared A. flavus A3.2890 spore suspensions. TLC analyses were performed for AFs extracted from the media. We observed that none of these treatments had any significant effect on AF production. No AF production was observed in any of the high initial spore density cultures (Figure 7). These results suggest that the inhibited AF biosynthesis in high initial spore density cultures was unlikely caused by reduced levels of TCA cycle intermediates.

Bottom Line: Metabolomic studies revealed that, in addition to inhibited AF biosynthesis, mycelia grown in peptone media with a high initial spore density showed suppressed fatty acid biosynthesis, reduced tricarboxylic acid (TCA) cycle intermediates, and increased pentose phosphate pathway products.Additions of TCA cycle intermediates had no effect on AF biosynthesis, suggesting the inhibited AF biosynthesis was not caused by depleted TCA cycle intermediates.This switching ability may offer Aspergillus species a competition advantage in natural ecosystems, producing AFs only when self-population is low and food is scarce.

View Article: PubMed Central - HTML - PubMed

Affiliation: Practaculture College, Gansu Agricultural University, Lanzhou 730070, China.

ABSTRACT

Background: Aflatoxins (AFs) are highly carcinogenic compounds produced by Aspergillus species in seeds with high lipid and protein contents. It has been known for over 30 years that peptone is not conducive for AF productions, although reasons for this remain unknown.

Results: In this study, we showed that when Aspergillus flavus was grown in peptone-containing media, higher initial spore densities inhibited AF biosynthesis, but promoted mycelial growth; while in glucose-containing media, more AFs were produced when initial spore densities were increased. This phenomenon was also observed in other AF-producing strains including A. parasiticus and A. nomius. Higher peptone concentrations led to inhibited AF production, even in culture with a low spore density. High peptone concentrations did however promote mycelial growth. Spent medium experiments showed that the inhibited AF production in peptone media was regulated in a cell-autonomous manner. mRNA expression analyses showed that both regulatory and AF biosynthesis genes were repressed in mycelia cultured with high initial spore densities. Metabolomic studies revealed that, in addition to inhibited AF biosynthesis, mycelia grown in peptone media with a high initial spore density showed suppressed fatty acid biosynthesis, reduced tricarboxylic acid (TCA) cycle intermediates, and increased pentose phosphate pathway products. Additions of TCA cycle intermediates had no effect on AF biosynthesis, suggesting the inhibited AF biosynthesis was not caused by depleted TCA cycle intermediates.

Conclusions: We here demonstrate that Aspergillus species grown in media with peptone as the sole carbon source are able to sense their own population densities and peptone concentrations to switch between rapid growth and AF production. This switching ability may offer Aspergillus species a competition advantage in natural ecosystems, producing AFs only when self-population is low and food is scarce.

Show MeSH