ARS | Publication request: Genomics of Aspergillus Spp for Controlling Harmful Toxins and Harnessing Beneficial Metabolites

Submitted to: Meeting Abstract
Publication Acceptance Date: June 1, 2004
Publication Date: July 31, 2004
Citation: Bhatnagar, D., Yu, J., Cleveland, T.E. Genomics Of Sspergillus Species For Controlling Harmful Toxins And Harnessing Beneficial Metabolites [abstract]. Society Of Industrial Microbiology Annual Meeting, July 25-29, 2004, Anaheim, California.

Technical Abstract: Aflatoxins are the most potent natural carcinogens produced primarily by the filamentous fungi, Aspergillus flavus and A. parasiticus. These fungi infect both pre-harvest crops and post-harvest commodities and contaminate them with aflatoxins. Genomics of aflatoxigenic fungi began with molecular understanding of the biosynthesis of aflatoxins. This process is very complex involving over two dozen enzymes. Studies on the molecular mechanism of aflatoxin B1 biosynthesis have identified at least 25 genes within a 70 Kb well-organized aflatoxin pathway gene cluster, including a positive regulatory gene for transcriptional activation of the structural genes. A sugar utilization gene cluster consisting of four genes has also been identified adjacent to the aflatoxin gene cluster, and additionally a nitrogen utilization gene cluster consisting of two genes has been identified somewhere in the genome. The completed DNA sequence of the 70 Kb aflatoxin gene cluster has been determined and the genes involved in aflatoxin formation have been systematically renamed from aflA, aflB, to aflY according to the convention of gene nomenclature for the genus Aspergillus. Genomic studies on A. flavus have been further extended to understand the molecular mechanisms that govern the regulation of aflatoxin biosynthesis, plant-fungal interaction, and evolutionary biology of aflatoxigenic fungi. The A. flavus Expressed Sequenced Tag (EST) project has been successfully executed at this lab. About 70%-80% total genes within the A. flavus genome have been identified (7,214 unique EST sequences) from a normalized cDNA library. Among the 7,214 unique ESTs, 3,728 tentative consensus (TC) sequences are assembled and 3,486 singleton sequences are identified from 22,324 usable sequences obtained. An A. flavus gene index has been constructed on the basis of these identified unique genes. Microarray containing all of these unique genes has been constructed. Additionally, the A. flavus EST profile has been compared to the A. oryzae EST data (provided by the Japanese Consortium on A. oryzae genome project). The application of EST/Microarray technologies for functional genomics studies is expected to provide vital information for developing new strategies for the control of aflatoxin contamination of crops and for harnessing other biochemical processes of these fungi that can be exploited for industrial applications. Funds have recently been obtained to carry out the whole genome sequencing of A. flavus by Prof. Gary Payne, North Carolina State University, in collaboration with our lab. Genome sequencing of other Aspergilli (such as A. niger, A. nidulans, and A. fumigatus) is also being undertaken at various labs in Europe and the U.S.