Adhesion of the Entomopathogenic Fungus <i>Beauveria</i> ( <i>Cordyceps</i> ) <i>bassiana</i> to Substrata

TLDR

The entomopathogenic fungus Beauveria bassiana produces three distinct propagules—aerial conidia, vegetative blastospores, and submerged conidia—that can be isolated from agar plates, rich broth cultures, and nutrient‑limited submerged cultures. The study aimed to determine how variations in cell surface properties of these propagules influence their adhesion, with the goal of guiding rational design to improve fungal efficacy and host specificity. Fluorescently labeled cells were used to quantify adhesion kinetics of each propagule type on surfaces with differing hydrophobic or hydrophilic characteristics. Aerial conidia adhered rapidly to hydrophobic and hydrophilic surfaces but were easily washed off, blastospores bound poorly to hydrophobic surfaces and required longer incubation for weakly polar surfaces, submerged conidia adhered broadly to all surface types, and adhesion patterns varied with glycosidase, protease, pH, carbohydrate competitors, detergents, and the presence of hydrophobin‑like proteins on aerial conidia.

Abstract

ABSTRACT The entomopathogenic fungus Beauveria bassiana produces at least three distinct single-cell propagules, aerial conidia, vegetative cells termed blastospores, and submerged conidia, which can be isolated from agar plates, from rich broth liquid cultures, and under nutrient limitation conditions in submerged cultures, respectively. Fluorescently labeled fungal cells were used to quantify the kinetics of adhesion of these cell types to surfaces having various hydrophobic or hydrophilic properties. Aerial conidia adhered poorly to weakly polar surfaces and rapidly to both hydrophobic and hydrophilic surfaces but could be readily washed off the latter surfaces. In contrast, blastospores bound poorly to hydrophobic surfaces, forming small aggregates, bound rapidly to hydrophilic surfaces, and required a longer incubation time to bind to weakly polar surfaces than to hydrophilic surfaces. Submerged conidia displayed the broadest binding specificity, adhering to hydrophobic, weakly polar, and hydrophilic surfaces. The adhesion of the B. bassiana cell types also differed in sensitivity to glycosidase and protease treatments, pH, and addition of various carbohydrate competitors and detergents. The outer cell wall layer of aerial conidia contained sodium dodecyl sulfate-insoluble, trifluoroacetic acid-soluble proteins (presumably hydrophobins) that were not present on either blastospores or submerged conidia. The variations in the cell surface properties leading to the different adhesion qualities of B. bassiana aerial conidia, blastospores, and submerged conidia could lead to rational design decisions for improving the efficacy and possibly the specificity of entomopathogenic fungi for host targets.