Metarhizium acridum exhibits a different conidial hydrophobicity than other insect-pathogenic fungi

Abstract

Metarhizium acridum is an insect-pathogenic fungus with a narrow host range that is used to control grasshoppers, locusts, and crickets. Its conidia show impressive resilience against UV-B radiation and heat compared to other insect pathogens. Despite this high tolerance, M. acridum is notably susceptible to various chemical stressors. The conidial surface is a monolayer formed by hydrophobins and the first barrier against stressors. However, little is known about the conidial surface properties of this fungus. This work aimed to evaluate the hydrophobic properties of the conidial surface in M. acridum ARSEF 324 and to compare them with those of other entomopathogen fungi. For this, drop profiles of water and diiodomethane on fungal cultures were analyzed, and the conidial hydrophobicity was estimated from a contact angle following the sessile drop method. The analysis of droplet profiles revealed distinct hydrophobic properties among the conidia of various insect-pathogenic fungi. The conidia of Beauveria bassiana, M. acridum, and Metarhizium robertsii exhibited high hydrophobicity, as indicated by water contact angles greater than 140°. In contrast, the conidia of Tolypocladium inflatum showed slightly lower hydrophobicity with a water contact angle below 130°. The behavior of diiodomethane further highlighted the variation in surface interactions, particularly for M. acridum, where the drop flattened instantly, indicating its low affinity for nonpolar compounds, which correlated with the extremely low tolerance of ARSEF 324 to chemicals. Overall, the study provides a deeper understanding of fungal surface properties, which could have implications for its tolerance to chemical stressors.