Microbiota in insect fungal pathology

Abstract

Significant progress has been made in the biochemical and genetic characterization of the host-pathogen interaction mediated by insect pathogenic fungi, with the most widely studied being the Ascomycetes (Hypocrealean) fungi, Metarhizium robertsii and Beauveria bassiana. However, few studies have examined the consequences and effects of host (insect) microbes, whether compatible or antagonistic, on the development and survival of entomopathogenic fungi. Host microbes can act on the insect cuticular surface, within the gut, in specialized insect microbe hosting structures, and within cells, and they include a wide array of facultative and/or obligate exosymbionts and endosymbionts. The insect microbiome differs across developmental stages and in response to nutrition (e.g., different plant hosts for herbivores) and environmental conditions, including exposure to chemical insecticides. Here, we review recent advances indicating that insect-pathogenic fungi have evolved a spectrum of strategies for exploiting or suppressing host microbes, including the production of antimicrobial compounds that are expressed at discrete stages of the infection process. Conversely, there is increasing evidence that some insects have acquired microbes that may be specialized in the production of antifungal compounds to combat infection by (entomopathogenic) fungi. Consideration of the insect microbiome in fungal insect pathology represents a new frontier that can help explain previously obscure ecological and pathological aspects of the biology of entomopathogenic fungi. Such information may lead to novel approaches to improving the efficacy of these organisms in pest control efforts.

Host–pathogen interaction after infection of Galleria mellonella with the filamentous fungus Beauveria bassiana

“…The filamentous fungus Beauveria bassiana is a natural pathogen of the greater wax moth Galleria mellonella . It has developed mechanisms facilitating access to the insect body via the cuticle (Boucias et al ., ). Attached to the cuticle, the fungus secretes enzymes: proteases, chitinases, and lipases, which digest insect body's cover and simultaneously exert the mechanical pressure on host's tissues (Butt et al ., ).…”

“…Recently, genes involved in B. bassiana infection of G. mellonella have been identified (Fan et al ., ; Chen et al ., ). The set of genes whose expression level changes upon the infectious process depends on the host (Zhou et al ., )…”

Characterization of a fungal competition factor: Production of a conidial cell-wall associated antifungal peptide

“…However, the underlying genetic mechanism(s) responsible for these activities have yet to be reported. The diverse ecological niches occupied by B. bassiana necessitates contact with a diverse range of competing microbes [38], however, again, little is known concerning the genetic mechanisms that have evolved to successfully compete in these environments. The characterization of the production of the secondary metabolite oosporein, as an antibacterial agent specifically after the death of the host, in order to maximally utilize the nutrient on the cadaver and successfully sporulate is one exception [39].…”

The Thm1 Zn(II)2Cys6 transcription factor contributes to heat, membrane integrity and virulence in the insect pathogenic fungus Beauveria bassiana

“…Studies on these entomopathogenic fungi, typified by the members of the Metarhizium and Beauveria genera, are gradually being regarding as model systems applicable to uncovering fundamental aspects of fungal development, stress response and virulence, particularly as these fungi display shared and unique attributes in comparison to plant and animals pathogens (Lu and St Leger, 2016;Wang et al, 2016;Zeng et al, 2017). B. bassiana is both a broad host range insect pathogen and a plant mutualist (Boucias et al, 2018;Moonjely et al, 2018). Infection occurs via adhesion of fungal conidia to the cuticle of the insect and subsequent direct penetration of the exoskeleton (Ortiz-Urquiza and .…”