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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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High initial spore densities repressed the expressions of AF biosynthesis genes inA. flavus. qRT-PCR was used to analyze expressions of AF production regulators (aflR and aflS) and AF biosynthesis genes (aflO, cypA, ordA and nadA) by A. flavus A3.2890 cultured in PMS media with 104 or 106 spores/ml for 2 (A) or 3 days (B). The relative expressions were quantified by the expression level of the β-Tubulin gene. Note the expression of nadA was not repressed in the high initial spore density culture.
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Figure 4: High initial spore densities repressed the expressions of AF biosynthesis genes inA. flavus. qRT-PCR was used to analyze expressions of AF production regulators (aflR and aflS) and AF biosynthesis genes (aflO, cypA, ordA and nadA) by A. flavus A3.2890 cultured in PMS media with 104 or 106 spores/ml for 2 (A) or 3 days (B). The relative expressions were quantified by the expression level of the β-Tubulin gene. Note the expression of nadA was not repressed in the high initial spore density culture.

Mentions: To further study how initial spore densities affect AF production in A. flavus, expression of AF biosynthesis-related genes was examined by quantitative reverse transcription PCR (qRT-PCR) in mycelia initiated with 104 or 106 spores/ml for two days. We observed that the expression levels of two transcriptional regulators (alfR and alfS), and three AF biosynthesis genes (aflO, cypA and ordA) from the AF biosynthesis gene cluster were substantially lower in mycelia initiated with 106 spores/ml, as compared to those initiated with 104 spores/ml (Figure 4A). The differences were even more pronounced on the day three (Figure 4B), suggesting transcriptional activation of AF biosynthesis in cultures initiated with the low spore density. We noted that nadA, which is involved in the conversion of AFG1 [47], showed increased expression in the culture initiated with 106 spores/ml, compared to those initiated with 104 spores/ml on the day three (Figure 4B).


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)

High initial spore densities repressed the expressions of AF biosynthesis genes inA. flavus. qRT-PCR was used to analyze expressions of AF production regulators (aflR and aflS) and AF biosynthesis genes (aflO, cypA, ordA and nadA) by A. flavus A3.2890 cultured in PMS media with 104 or 106 spores/ml for 2 (A) or 3 days (B). The relative expressions were quantified by the expression level of the β-Tubulin gene. Note the expression of nadA was not repressed in the high initial spore density culture.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: High initial spore densities repressed the expressions of AF biosynthesis genes inA. flavus. qRT-PCR was used to analyze expressions of AF production regulators (aflR and aflS) and AF biosynthesis genes (aflO, cypA, ordA and nadA) by A. flavus A3.2890 cultured in PMS media with 104 or 106 spores/ml for 2 (A) or 3 days (B). The relative expressions were quantified by the expression level of the β-Tubulin gene. Note the expression of nadA was not repressed in the high initial spore density culture.
Mentions: To further study how initial spore densities affect AF production in A. flavus, expression of AF biosynthesis-related genes was examined by quantitative reverse transcription PCR (qRT-PCR) in mycelia initiated with 104 or 106 spores/ml for two days. We observed that the expression levels of two transcriptional regulators (alfR and alfS), and three AF biosynthesis genes (aflO, cypA and ordA) from the AF biosynthesis gene cluster were substantially lower in mycelia initiated with 106 spores/ml, as compared to those initiated with 104 spores/ml (Figure 4A). The differences were even more pronounced on the day three (Figure 4B), suggesting transcriptional activation of AF biosynthesis in cultures initiated with the low spore density. We noted that nadA, which is involved in the conversion of AFG1 [47], showed increased expression in the culture initiated with 106 spores/ml, compared to those initiated with 104 spores/ml on the day three (Figure 4B).

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