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Appl. Environ. Microbiol. doi:10.1128/AEM.00565-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Morphological transitions governed by density dependence and lipoxygenase activity in Aspergillus flavus

Department of Plant Pathology, University of Wisconsin - Madison, 1550 Linden Dr., Madison, WI 53706-1598; Department of Medical Microbiology and Immunology

^* To whom correspondence should be addressed. Email: npk{at}plantpath.wisc.edu.

	Abstract

Aspergillus flavus differentiates to produce asexual dispersing spores (conidia) or overwintering survival structures called sclerotia. Results here show both processes are oppositely regulated by density dependent mechanisms where increasing cell density (from 10¹ to 10⁷ cells) yields lowest sclerotial and highest conidial numbers. Extract from spent medium of low cell density cultures induced a high sclerotial phenotype whereas high cell density extract increased conidiation. Density dependent development is also modified by changes in lipid availability. Exogenous linoleic acid increased sclerotial production at intermediate cell densities (10⁴ and 10⁵ cells) whereas oleic and linolenic fatty acids inhibited sclerotia formation. Deletion of Aflox encoding a lipoxygenase (LOX) greatly diminished density dependent development of both sclerotia and conidia with an overall increase in sclerotia and decrease in conidia at high cell densities (>10⁵ cells). The Aflox mutants showed decreased linoleic acid LOX activity. Taken together, these results suggest a quorum sensing mechanism where a factor(s) produced in dense cultures, perhaps a LOX derived metabolite, activates conidial formation while a factor(s) produced in low density cultures stimulates sclerotia formation.