Identification and characterization of the Aspergillus flavus aspergillic acid gene cluster

J. Carya, M. Lebara, C. Carter-Wientjesa, B. Macka, R. Majumdara, J. Diana Di Mavungub and S. De Saegerb

Author address: 

aUSDA-ARS-SRRC, New Orleans, LA bLaboratory of Food Analysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium


Aspergillus flavus produces toxic and carcinogenic aflatoxins. In silico analysis of the A. flavus genome
revealed 56 gene clusters encoding for secondary metabolites (SMs). Although about 20 SMs have been
identified from A. flavus cultures, studies by our group and others have experimentally assigned
metabolites to just ten A. flavus gene clusters. We are interested in how these SMs affect fungal
development, survival, and virulence. We are particularly interested in A. flavus metabolites that are
produced during infection of corn seed. RNA-Seq analysis of all predicted A. flavus secondary metabolic
gene cluster ‘backbone’ genes during corn kernel infection showed that in addition to the aflatoxin cluster
polyketide synthase (PKS) gene, aflC, one of the earliest genes expressed was the uncharacterized
Cluster 11 nonribosomal peptide synthetase (NRPS) gene, asaB (AFLA_023020). SMURF analysis
indicated that Cluster 11 may be composed of as many as 12 genes, however we focused on five genes
encoding the putative NRPS, desaturase, P450 oxidoreductase, MFS transporter and C6 transcription
factor. LC-MS analysis of extracts from knockout mutants of these genes showed that they were
responsible for the synthesis of the previously characterized pyrazinone, deoxyaspergillic acid (deoxy-
AA), and the antimicrobial hydroxamic acid-containing mycotoxins aspergillic acid (AA) and hydroxy-AA
(OH-AA). From the LC-MS data we have proposed a biosynthetic pathway for the production of these
metabolites. In addition, we found that AA can form a trimer with one atom of iron to generate
ferriaspergillin, perhaps indicating that this cluster is involved in regulation of iron homeostasis in A.


abstract No: 


Full conference title: 

The Fourteenth International Aspergillus Meeting, Asilomar Conference Center, Pacific Grove, CA, USA
    • Asperfest 14 (2017)