Quorum sensing activity in Ophiostoma ulmi: effects of fusel oils and branched chain amino acids on yeast-mycelial dimorphism

Authors

A. Berrocal, Universidad del Bio-Bio
J. Navarrete, Universidad del Bio-BioFollow
C. Oviedo, Universidad del Bio-Bio
K. W. Nickerson, University of Nebraska - LincolnFollow

Date of this Version

2012

Document Type

Article

Citation

Journal of Applied Microbiology 113, pp. 126–134. doi:10.1111/j.1365-2672.2012.05317.x

Comments

Copyright 2012 The Society for Applied Microbiology. Used by permission.

Abstract

Aims: For Ophiostoma (Ceratocystis) ulmi, the ability to undergo morphological change is a crucial factor for its virulence. To gain an understanding of quorum- sensing activity in O. ulmi as it relates to yeast-mycelium dimorphism control, this study examines the effects of branched-chain amino acids as well as their fusel alcohols and fusel acids as quorum sensing molecules.

Methods and Results: In a defined medium containing glucose, proline and salts, O. ulmi grew as yeasts when the culture was inoculated with a high density of spores (2-10⁷ CFU ml^-1) and as mycelia when inoculated with a low spore density (4-10⁵ CFU ml^-1). The cultures displaying yeast morphology secreted a quorum-sensing factor that shifted the morphology from mycelia to yeast. This quorum-sensing molecule was lipophilic and extractable by organic solvents from the spent medium. Using GC⁄MS analysis, it was determined that the major compound in the extract was 2-methyl-1-butanol. A similar effect was observed when the branched-chain amino acids (fusel alcohol precursors) were used as the nitrogen source. E, E-farnesol had no effect on the morphology of O. ulmi.

Conclusions: Addition of the branched-chain amino acids or one of the compounds detected in the spent medium, 2-methyl-1-butanol or 4-hydroxyphenylacetic acid, or methylvaleric acid, decreased germ tube formation by more than 50%, thus demonstrating a quorum sensing molecule behavior in O. ulmi cultures.

Significance and impact of the study: This study presents advances in the investigation of dimorphism in O. ulmi, complementing the existing scientific basis, for studying, understanding and controlling this phenomenon.