The role of the rodlet structure on the physicochemical properties of Aspergillus conidia

Physico-chemical properties of Aspergillus conidia rely on their outer cell -wall rodlet layer. In A. fumigatus and A. nidulans, the rodlet structure i s due to an hydrophobin encoded by homologous rodA genes. To evaluate the r ole of the rodlet structure on the physico-chemical properties of conidia, we compared hydrophobicity, Lewis acid-base (i.e. electron donor/acceptor) characteristics and electrostatic charge of hydrophobin-less (rodletless) m utant and wild-type conidia of A. fumigatus and A. nidulans. The results ob tained by aqueous-solvent partitioning assays, microsphere adhesion assays and microelectrophoresis showed that the disruption of the rodA gene modifi es surface properties of A. fumigatus and A. nidulans conidia, and confirme d that the rodlet layer plays a key role in their physico-chemical behaviou r. The absence of this layer on A. fumigatus spores led to the appearance o f weakly basic and acidic characteristics, and had a slight effect on the h ydrophobicity of conidia. Whereas in A. nidulans, it induced a basic charac ter, a marked decrease in hydrophobicity and in the polarization capacity ( electronegativity) of conidia. These physico-chemical differences between A . fumigatus and A. nidulans rodletless conidia may be attributed to differe nces in the composition of the conidial outer cell-wall of the two species.