Title: Conversion of fusaric acid to fusarinol by Aspergillus niger: A detoxification reaction Authors
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 26, 2013
Publication Date: January 22, 2014
Citation: Crutcher, F.K., Liu, J., Puckhaber, L.S., Stipanovic, R.D., Duke, S.E., Bell, A.A., Williams, H., Nichols, R. 2014. Conversion of fusaric acid to fusarinol by Aspergillus niger: A detoxification reaction. Journal of Chemical Ecology. 40:84-89. Interpretive Summary: New isolates of the plant pathogen Fusarium oxysporum f. sp. vasinfectum that are highly pathogenic to cotton have been identified in California and Australia. These isolates produce very high levels of the plant toxin fusaric acid compared to traditional less pathogenic isolates previously found in the U.S. To understand the pathogenicity process of these new isolates, we have investigated how other soil microbes detoxify fusaric acid. We now report that a soil microbe, Aspergillus niger, converts fusaric acid into a less pathogenic compound in which the carboxylic acid group present in fusaric acid is converted into an alcohol. We had previously shown that if the carboxylic acid group is removed the resulting compound is also less toxic to cotton than fusaric acid. Thus, it appears that the carboxylic acid group plays an important role in the pathogenicity of fusaric acid.
Technical Abstract: The fungus Fusarium oxysporum causes wilt diseases of plants and produces a potent phytotoxin fusaric acid (FA) which is also toxic to many microorganisms. An Aspergillus strain with high tolerance to FA was isolated from soil. HPLC analysis of culture filtrates from A. niger grown with the addition of FA indicated the formation of a degradation product over time associated with the decrease of FA. Spectral analysis and chemical synthesis confirmed the compound as 5-butyl-2-pyridinemethanol, referred to here as fusarinol. The phytotoxicity of fusarinol compared to FA was measured by comparing necrosis induced in cotton (Gossypium hirsutum L. cv. Coker 312) cotyledons. Fusarinol was significantly less phytotoxic than FA. Therefore, the A. niger strain provides a novel detoxification mechanism against FA which may be utilized to control Fusarium wilt.