Biofilm formation by the fungus Phaeomoniella chlamydospora: a causal agent of esca disease of grapevine

The present study suggests that the Esca pathogenic fungus Phaeomoniella chlamydospora can form biofilm in vitro and possibly in the grapevine host tissues. This phenomenon was revealed by the detailed examination of the development of three isolates of the fungus, showing dimorphic growth with the formation of yeast-like cells in the center, which were embedded in a polysaccharide-rich extracellular matrix, and filamentous growth at the colony margins. The colonies produced acetate, which chemical proved to be an enhancer of yeast-like growth and extracellular matrix production. The dynamic of biofilm formation was correlated with the ability of the strains to produce acetate, suggesting that it acts as a quorum sensing molecule in the process. The dimorphic growth of P. chlamydospora was also demonstrated in host tissues as a sole nutrient source, suggesting that biofilm can be produced in planta and take part in the pathogenesis of Esca. The biofilms formed by the fungus may contribute to the previously reported inhibition of sap flow in the infected plants, while its quorum sensing-mediated nature may partly explain the controversial literature data on the occurrence of the pathogen and symptom severity in the host.