The entomogenous filamentous fungus, Beauveria bassiana expresses two hydrophobin genes, hyd1 and hyd2, hypothesized to be involved in cell surface hydrophobicity, adhesion, virulence, and to constitute the protective spore coat structure known as the rodlet layer. Targeted gene inactivation of hyd1 resulted in seemingly 'bald' conidia that contained significantly altered surface fascicles or bundles. These cells displayed decreased spore hydrophobicity, loss of water mediated dispersal, changes in surface carbohydrate epitopes and β-1,3-glucan distribution, lowered virulence in insect bioassays, but no effect on adhesion. In contrast, Δhyd2 mutants retained distorted surface bundles, but truncated/incomplete rodlets could be seen within the bundles. Δhyd2 conidia displayed both decreased cell surface hydrophobicity and adhesion, but the mutant was unaffected in virulence. The double Δhyd1Δhyd2 mutant was distinct from the single mutants, lacking both bundles and rodlets, and displaying additively decreased cell surface hydrophobicity, reduced cell attachment and lowered virulence than the Δhyd1 mutant. Epitope tagged constructs of the proteins were used to examine the expression and distribution of the proteins and to demonstrate the continued presence of Hyd2 in the Δhyd1 strain and vice versa. The implications of our results with respect to fascicle and rodlet assembly on the spore surface are discussed.
© 2011 Blackwell Publishing Ltd.