Alkane-grown Beauveria bassiana produce mycelial pellets displaying peroxisome proliferation, oxidative stress, and cell surface alterations

Abstract

The entomopathogenic fungus Beauveria bassiana is able to grow on insect cuticle hydrocarbons, inducing alkane assimilation pathways and concomitantly increasing virulence against insect hosts. In this study, we describe some physiological and molecular processes implicated in growth, nutritional stress response, and cellular alterations found in alkane-grown fungi. The fungal cytology was investigated using light and transmission electron microscopy while the surface topography was examined using atomic force microscopy. Additionally, the expression pattern of several genes associated with oxidative stress, peroxisome biogenesis, and hydrophobicity were analysed by qPCR. We found a novel type of growth in alkane-cultured B. bassiana similar to mycelial pellets described in other alkane-free fungi, which were able to produce viable conidia and to be pathogenic against larvae of the beetles Tenebrio molitor and Tribolium castaneum. Mycelial pellets were formed by hyphae cumulates with high peroxidase activity, exhibiting peroxisome proliferation and an apparent surface thickening. Alkane-grown conidia appeared to be more hydrophobic and cell surfaces displayed different topography than glucose-grown cells. We also found a significant induction in several genes encoding for peroxins, catalases, superoxide dismutases, and hydrophobins. These results show that both morphological and metabolic changes are triggered in mycelial pellets derived from alkane-grown B. bassiana.

The entomopathogenic fungus Beauveria bassiana produces microsclerotia‐like pellets mediated by oxidative stress and peroxisome biogenesis

“…Cross section of B. bassiana propagules stained with 3,3′‐diaminobenzidine (DAB) at 30 000× magnification, following the full protocol described by Huarte‐Bonnet and colleagues (). A. Mycelia (used as control) exhibiting the DAB reaction mainly in vacuoles.…”

“…B. Peroxin genes associated with peroxisomal biogenesis. Total RNA extraction, cDNA synthesis and qPCR were performed by the same kits and following the same procedures described by Huarte‐Bonnet and colleagues (). Primers for the selected marker genes and PCR efficiencies are listed in Supporting Information Table S4.…”

“…By transcriptomic approaches, some authors proposed that oxidative stress is linked with microsclerotial development in which the iron ion (Fe +2 ) plays an important role during its formation (Georgiou et al ., ; Song et al ., ). Although no transcriptomic analyses are available to shed light into the gene expression profile in the formation of either microsclerotia or mycelial pellets in B. bassiana , Huarte‐Bonnet and colleagues () recently reported that B. bassiana formed conspicuous mycelial pellets in which key antioxidant enzymes were associated with the oxidative metabolism during this morphogenetic growth process when the fungus was grown in hydrocarbon‐enriched liquid medium as the sole carbon source. This new finding has opened a new opportunity to explore medium optimization for B. bassiana microsclerotial production and its further use in controlling soil‐dwelling arthropod pests of agriculturally economic importance.…”

The second International Symposium on Fungal Stress: ISFUS

“…For the award competitions, students submitted original research articles formatted for journal publication. Two of these articles are featured in this special issue (Huarte-Bonnet et al, 2017b;Muniz et al, 2017). The award winners also gave oral presentations at ISFUS.…”

“…The ISFUS-2017 Abstracts Book, which feature abstracts from the presentations and posters, is available in the Electronic Supplementary Material 1 of this article. Articles highlighting the contributions to the conference are published in this Fungal Biology special issue entitled "Biology of Fungal Systems under Stress", which focuses on cellular biology, ecology, environment, agriculture, medical mycology, and biotechnology in the context of fungal stress biology (Chen et al, 2017;Ferreira et al, 2017;Huarte-Bonnet et al, 2017b;Keyhani, 2017;Malo et al, 2017;Muniz et al, 2017;Tonani et al, 2017).…”