Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 19, 2003
Publication Date: October 1, 2003
Citation: Yu, J., Mohawed, S.M., Bhatnagar, D., Cleveland, T.E. 2003. Substrate-induced Lipase Gene Expression and Aflatoxin Production in Aspergillus parasiticus and Aspergillus flavus. Journal of Applied Microbiology. 95(6):1334-1342. Interpretive Summary: Aflatoxins are natural compounds produced by the two common molds, Aspergillus flavus and A. parasiticus. These toxins contaminate agricultural commodity such as corn, cotton, peanuts, and treenuts resulting in either significant economic losses or food safety problems. Our efforts are focused on the elucidation of the mechanism of aflatoxin production. In order to better understand the nutritional factors affecting aflatoxin formation, we cloned a lipase gene (lipA) from toxigenic fungi. The expression of the lipase gene under diverse nutritional conditions has been studied. The understanding of the expression and regulation of lipase gene in relation to aflatoxin production may provide insight into evolution biology and how to interrupt the process of aflatoxin production in fungi. This information may help in devising strategies to reduce or eliminate aflatoxin contamination in the food and feed.
Technical Abstract: Alfatoxins are toxic metabolites with demonstrated carcinogenic activity in vertebrate systems produced by Aspergillus flavus and A. parasiticus when these fungi infect corn, cotton, peanuts and tree nuts. Lipid metabolism has been demonstrated to be utilized by fungi to as nutrition for growth and secondary metabolism. Enzymes involved in lipid metabolism produced by fungi, such as lipases, may be involved in the course of fungal invasion and subsequent growth as well as aflatoxin formation. We have cloned a gene, lipA, from aflatoxin-producing fungal species A. flavus and A. parasiticus, that encodes a lipase involved in the breakdown of lipids. The expression of the lipase gene (mature mRNA) under substrate induced conditions correlated well with aflatoxin production in aflatoxigenic species A. flavus (SRRC 1007) and A. parasiticus (SRRC 143). In the two non-aflatoxigenic A. flavus isolates, wool-1 and wool-2, no aflatoxin was produced under both aflatoxin-conducive and lipase-induced media conditions. The sequence of the lipA gene and its expression patterns in the two non-toxigenic A. flavus isolates were shown to be the same as that of toxigenic A. flavus. Both lipid and hexose support aflatoxin formation through independently regulated pathways. Unlike the aflatoxin pathway genes, in which the regulation of gene expression is at the transcriptional level in the presence of a pathway regulator, the lipid metabolism pathway gene, lipA, is demonstrated to be regulated at the post-transcriptional level, specifically, controlling the processing of introns.