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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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Spore density-dependent AF productions inA. flavusin PMS media. (A, B), TLC analyses of AF productions by A. flavus A3.2890 cultured in GMS (A) or PMS (B) media for 3 days with initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Ten μl AF extracts were loaded in (A), and 50 μl in (B). St: AF standards. (C, D) HPLC analyses of AFs produced by A. flavus A3.2890 cultured in GMS (C) or PMS (D) media for 3 days, with the initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Note in GMS media both AFB1 and AFG1 were produced, while in PMS media mainly AFG1 was produced. (E) The time course of AFG1 productions in PMS media during 5-day cultures, with initial spore densities of 106 (dotted line) or 104 (solid line) spores/ml. All results were the mean ± SD of 3 measurements from mixed three independent samples.
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Figure 1: Spore density-dependent AF productions inA. flavusin PMS media. (A, B), TLC analyses of AF productions by A. flavus A3.2890 cultured in GMS (A) or PMS (B) media for 3 days with initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Ten μl AF extracts were loaded in (A), and 50 μl in (B). St: AF standards. (C, D) HPLC analyses of AFs produced by A. flavus A3.2890 cultured in GMS (C) or PMS (D) media for 3 days, with the initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Note in GMS media both AFB1 and AFG1 were produced, while in PMS media mainly AFG1 was produced. (E) The time course of AFG1 productions in PMS media during 5-day cultures, with initial spore densities of 106 (dotted line) or 104 (solid line) spores/ml. All results were the mean ± SD of 3 measurements from mixed three independent samples.

Mentions: PMS has long been considered to be a non-conducive medium for AF production in both A. flavus and A. parasiticus[23-25]. To investigate the mechanism underlying peptone’s influence on AF biosynthesis, the well-studied A. flavus A3.2890 [37-39] from the China General Microbiological Culture Collection Center (CGMCC) was used to conduct our experiments. It was indeed the case that A. flavus did not produce AFs when cultured at the commonly employed initial spore density of 105 or 106 spores/ml. However, when various spore densities of A. flavus were tested to initiate cultures, a density-dependent AF production was observed. When the initial spore density was gradually decreased, increasing amounts of AFs were detected in media after 3-day culture, as shown by thin-layer chromatography (TLC) and high pressure liquid chromatography (HPLC) analyses (Figure 1B & D). At 101 spores/ml, the amount of AFs produced was significantly lower, comparable to that of the 104 spores/ml culture. The maximal AF production was observed in the PMS medium inoculated with 102 spores/ml. This differs from GMS cultures, where increasing amounts of AFs were produced when initial spore densities were increased from 101 to 106 spores/ml (Figure 1A & C). We also observed that in GMS media, AFB1 was the major toxin (Figure 1C), while in PMS media, AFG1 was the primary toxin produced (Figure 1D). These data suggest that AF biosynthesis is regulated differentially in these two media.


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)

Spore density-dependent AF productions inA. flavusin PMS media. (A, B), TLC analyses of AF productions by A. flavus A3.2890 cultured in GMS (A) or PMS (B) media for 3 days with initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Ten μl AF extracts were loaded in (A), and 50 μl in (B). St: AF standards. (C, D) HPLC analyses of AFs produced by A. flavus A3.2890 cultured in GMS (C) or PMS (D) media for 3 days, with the initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Note in GMS media both AFB1 and AFG1 were produced, while in PMS media mainly AFG1 was produced. (E) The time course of AFG1 productions in PMS media during 5-day cultures, with initial spore densities of 106 (dotted line) or 104 (solid line) spores/ml. All results were the mean ± SD of 3 measurements from mixed three independent samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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Figure 1: Spore density-dependent AF productions inA. flavusin PMS media. (A, B), TLC analyses of AF productions by A. flavus A3.2890 cultured in GMS (A) or PMS (B) media for 3 days with initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Ten μl AF extracts were loaded in (A), and 50 μl in (B). St: AF standards. (C, D) HPLC analyses of AFs produced by A. flavus A3.2890 cultured in GMS (C) or PMS (D) media for 3 days, with the initial spore densities of 101, 102, 103, 104, 105 and 106 spores/ml. Note in GMS media both AFB1 and AFG1 were produced, while in PMS media mainly AFG1 was produced. (E) The time course of AFG1 productions in PMS media during 5-day cultures, with initial spore densities of 106 (dotted line) or 104 (solid line) spores/ml. All results were the mean ± SD of 3 measurements from mixed three independent samples.
Mentions: PMS has long been considered to be a non-conducive medium for AF production in both A. flavus and A. parasiticus[23-25]. To investigate the mechanism underlying peptone’s influence on AF biosynthesis, the well-studied A. flavus A3.2890 [37-39] from the China General Microbiological Culture Collection Center (CGMCC) was used to conduct our experiments. It was indeed the case that A. flavus did not produce AFs when cultured at the commonly employed initial spore density of 105 or 106 spores/ml. However, when various spore densities of A. flavus were tested to initiate cultures, a density-dependent AF production was observed. When the initial spore density was gradually decreased, increasing amounts of AFs were detected in media after 3-day culture, as shown by thin-layer chromatography (TLC) and high pressure liquid chromatography (HPLC) analyses (Figure 1B & D). At 101 spores/ml, the amount of AFs produced was significantly lower, comparable to that of the 104 spores/ml culture. The maximal AF production was observed in the PMS medium inoculated with 102 spores/ml. This differs from GMS cultures, where increasing amounts of AFs were produced when initial spore densities were increased from 101 to 106 spores/ml (Figure 1A & C). We also observed that in GMS media, AFB1 was the major toxin (Figure 1C), while in PMS media, AFG1 was the primary toxin produced (Figure 1D). These data suggest that AF biosynthesis is regulated differentially in these two media.

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