New Perspectives on Aflatoxin Biosynthesis

Bennett, Joan W.; Christensen, Siegfried B.

doi:10.1016/s0065-2164(08)70354-x

Cited by 137 publications

(76 citation statements)

References 189 publications

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“…Aflatoxins are polyketide-derived secondary metabolites produced via the following conversion path: acetate 3 polyketide 3 anthraquinones 3 xanthones 3 aflatoxins (3,6,11,15,102,120). The genes involved in the major conversion steps from early precursors to aflatoxins and their functions are discussed below.…”

Section: Genes In Aflatoxin Biosynthesismentioning

confidence: 99%

Clustered Pathway Genes in Aflatoxin Biosynthesis

Chang

Ehrlich

et al. 2004

Appl Environ Microbiol

720

595

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Section: Genes In Aflatoxin Biosynthesismentioning

confidence: 99%

Clustered Pathway Genes in Aflatoxin Biosynthesis

Chang

Ehrlich

et al. 2004

Appl Environ Microbiol

720

595

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“…The biosynthetic pathway of aflatoxins is generally accepted to be as follows : acetate/malonate + norsolorinic acid (NA) + averantin + averufin + versiconal hemiacetal acetate (VHA) + versicolorin A (VA) + sterigmatocystin (ST) + O-methylsterigmatocystin (OMST) + aflatoxin B1 (AFB,) (Bennett & Christensen, 1983;Bhatnagar et al, 1987;Dutton, 1988;Yabe et al, 19886). Fig.…”

Section: Introductionmentioning

confidence: 99%

A metabolic grid among versiconal hemiacetal acetate, versiconol acetate, versiconol and versiconal during aflatoxin biosynthesis

Yabe

Ando

Hamasaki

1991

Journal of General Microbiology

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Dichlorvos treatment of aflatoxigenic Aspergillus parasiticus SYS-4 (NRRL 2999) or a versicolorin Aaccumulating mutant, NIAH-9, resulted in accumulation of versiconol acetate (VOAc) and versiconal hemiacetal acetate (VHA), whereas the production of aflatoxins, versicolorin A (VA), and versiconol (VOH) decreased. In feeding experiments using another non-aflatoxigenic mutant, NIAH-26, aflatoxins were newly produced from each of VHA, VOAc, VOH, versicolorin B (VB) and versicolorin C (VC). In these experiments, aflatoxin production from VHA or VOAc was inhibited by dichlorvos, whereas that from each of VOH, VB and VC was insensitive to dichlorvos. In cell-free experiments using the cytosol fraction of NIAH-26, VHA was converted to VC (or VB) and a substance tentatively identified as versiconal (VHOH). By further addition of NADH or NADPH to the same reaction mixture, VOAc and VOH were also formed together with VC (VB) and VHOH. VOH was produced from VOAc irrespective of nicotinamide adenine nucleotide. Also, the incubation of VOH in the presence of NAD or NADP led to the formation of VC (VB). The production of VC (VB) and VHOH from VHA, and that of VOH from VOAc was inhibited by dichlorvos, whereas the production of VOAc from VHA, and that of VC (VB) from VOH, was insensitive to dichlorvos. These results indicate that a metabolic grid catalysed by dehydrogenase and esterase among VHA, VOAc, VOH and VHOH, and a reaction from VHOH to VC (VB) are involved in aflatoxin biosynthesis. These enzyme activities were also detected when yeast extract peptone medium was used, or when A. uryzae SYS-2 was examined.

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“…Aflatoxins (AFs) are a group of polyketide-derived mycotoxins produced by certain strains of Aspergillus parasiticus and A. flavus (10,27). As with other secondary metabolites, the biosynthesis of AFs occurs at the beginning of and during idiophase when growth of the molds has greatly slowed or stopped, while developmental and chemical differentiation ensue (27).…”

mentioning

confidence: 99%

Characterization of the polyketide synthase gene (pksL1) required for aflatoxin biosynthesis in Aspergillus parasiticus

1995

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Aflatoxins are potent toxic and carcinogenic compounds, produced by Aspergillus parasiticus and A. flavus as secondary metabolites. In this research, a polyketide synthase gene (pksL1), the key gene for aflatoxin biosynthesis initiation in A. parasiticus, has been functionally identified and molecularly characterized. PCRderived DNA probes were used to find the pksL1 gene from subtracted, aflatoxin-related clones. Gene knockout experiments generated four pksL1 disruptants which lost both the ability to produce aflatoxins B1, B2, and G1 and the ability to accumulate norsolorinic acid and all other intermediates of the aflatoxin biosynthetic pathway. A pksL1 DNA probe detected a 6.6-kb poly(A) ؉ RNA transcript in Northern (RNA) hybridizations. This transcript, associated with aflatoxin production, exhibited a regulated expression that was influenced by growth phase, medium composition, and culture temperature. DNA sequencing of pksL1 revealed an open reading frame for a polypeptide (PKSL1) of 2,109 amino acids. Sequence analysis further recognized four functional domains in PKSL1, acyl carrier protein, ␤-ketoacyl-acyl carrier protein synthase, acyltransferase, and thioesterase, all of which are usually present in polyketide synthases and fatty acid synthases. On the basis of these results, we propose that pksL1 encodes the polyketide synthase which synthesizes the backbone polyketide and initiates aflatoxin biosynthesis. In addition, the transcript of pksL1 exhibited heterogeneity at the polyadenylation site similar to that of plant genes.Aflatoxins (AFs) are a group of polyketide-derived mycotoxins produced by certain strains of Aspergillus parasiticus and A. flavus (10, 27). As with other secondary metabolites, the biosynthesis of AFs occurs at the beginning of and during idiophase when growth of the molds has greatly slowed or stopped, while developmental and chemical differentiation ensue (27). AFB 1 , AFB 2 , AFG 1 , and AFG 2 are the most abundant AFs (20). These toxic and carcinogenic compounds frequently contaminate food and feed commodities (3, 36). A typical AF, AFB 1 for example, is produced by the following generally accepted pathway: acetate building blocks (also hexanoate)3anthrone-derivative polyketide3norsolorinic acid (NA)3averanfin3averufin3hydroxyversicolorine3versiconal hemiacetal acetate3versicolorin B3versicolorin A3sterig-matocystin3o-methylsterigmatocystin3AFB 1 (13,15,27,58). NA is polyketide derived and represents the first stable intermediate in AF biosynthesis (34,37). An unstable anthronederivative polyketide has been proposed as a hypothetical intermediate formed prior to NA, but this theoretical polyketide has not been isolated, presumably because it is rapidly oxidized to NA (27).Genes involved in the initial steps of the pathway are still unknown; their identification and characterization are essential to understanding the initiation of AF biosynthesis (15). In the initial steps of AF biosynthesis, there is predicted to be a polyketide synthase (PKS), but the enzyme has not been is...

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New Perspectives on Aflatoxin Biosynthesis

Cited by 137 publications

References 189 publications

Clustered Pathway Genes in Aflatoxin Biosynthesis

Clustered Pathway Genes in Aflatoxin Biosynthesis

A metabolic grid among versiconal hemiacetal acetate, versiconol acetate, versiconol and versiconal during aflatoxin biosynthesis

Characterization of the polyketide synthase gene (pksL1) required for aflatoxin biosynthesis in Aspergillus parasiticus

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