The Role of Β-Galactofuranose in Cell Wall Surface Structure and Elasticity of Aspergillus Nidulans

Abstract

The fungal cell wall is a first line of defence from the external environment or chemical treatments. Glucan, chitin and mannan are the main components of Aspergillus nidulans hyphal cell wall. β-galactofuranose is a minor component of the cell wall and carries out crosslinking of the other cell wall components, therefore responsible for maintaining cell wall structural integrity. The objective of this study is to reveal the role of β-galactofuranose on structure and physical properties of the hyphal cell wall. Based on its unique capacity to image live samples, atomic force microscopy was used to determine both the ultrastructure and mechanical properties of the hyphal cell wall. Four different knock-out strains of Aspergillus nidulans (ugeAΔ, ugeBΔ ugeA/BΔ and ugmAΔ,) that compromise β-galactofuranose synthesis were compared with the wildtype strain (AAE1). Atomic force microscopic imaging and force spectroscopy the mutant wild type strains suggest that a lack of galactofuranose reduces the integrity of cell wall components, where the surface subunits of UgeAΔ and UgmAΔ are 2 times and 4 times larger than that of the wildtype(AAE1) respectively. UgeB shows similar sized subunits as AAE1, in direct contrast to the complete disruption of the structural organization for the cell wall surface of the double mutant ugeA/BΔ. The structural changes are accompanied by a change in viscoelasticity, where the wild type strain is the most elastic. We propose that the lack of galactofuranose disrupts the proper packing of cell wall components, giving rise to more disordered surface subunits and therefore greater pliability.