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

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 behaviour 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.

Quorum-Sensing Mechanisms Mediated by Farnesol in Ophiostoma piceae: Effect on Secretion of Sterol Esterase

“…Interestingly, other authors did not find any effect of farnesol on O. ulmi (4,26,33). In this sense, the O. piceae strain studied in this work is a saprophyte and affiliates phylogenetically with the nonpathogenic species of the Ophiostoma clade, such as O. quercus, far from the pathogens O. ulmi and O. novo-ulmi (see Fig.…”

“…Its ability to produce a morphological transition from yeast to hyphal forms, depending on fungal culture conditions, probably contributes to its adaptation to different environmental conditions (3). The effect of inoculum size on culture morphology of fungi from the genera Ophiostoma has been recently reported, suggesting that yeast-or hypha-like growth could be associated with quorum-sensing (QS) activity (4).…”

Quorum sensing activity and control of yeast-mycelium dimorphism in Ophiostoma floccosum

“…l-proline was the best N source for yeast production, with the dominant variable being an inoculum size ≥10 7 cells ml -1 . As expected from previous studies on related fungi (Hornby et al 2004;Berrocal et al 2012b), the high cell density which promoted yeast production was mediated by an extracellular lipophilic molecule or group of molecules termed QSMs. The ethyl acetate-extractable supernatants from the albino strain of O. floccosum contained both the biological activity to block mycelial growth and three cyclic sesquiterpenes (Figure 4) as identified by GC/ MS in comparison with the NIST 05 library.…”

“…This compound was lipophilic (Hornby et al 2004). Berrocal et al (2012b) found that the addition of 2-methyl-1-butanol or 3-methylvaleric acid (the fusel alcohol and fusel acid derived from isoleucine, respectively) or 4-hydroxyphenylacetic acid decreased the formation of germ tubes in O. ulmi cultures by more than 50%, thus demonstrating a QSM behavior. A similar effect was obtained using branched-chain amino acids (precursors of fusel alcohols) as N sources (Berrocal et al 2012b).…”

“…Some studies on the growth morphology of Ceratocystis (Ophiostoma) ulmi and Candida albicans in liquid culture media, found that their morphology was influenced by the cell density (Kulkarni and Nickerson 1981;Hornby et al 2001Hornby et al , 2004Berrocal et al 2012b). …”