A PCR-based tool for the cultivation-independent monitoring of Pandora neoaphidis

Pathogen-microbiome interactions and the virulence of an entomopathogenic fungus

Bacteria shape interactions between hosts and fungal pathogens. In some cases, bacteria associated with fungi are essential for pathogen virulence. In other systems, host-associated microbiomes confer resistance against fungal pathogens. We studied an aphid-specific entomopathogenic fungus called Pandora neoaphidis in the context of both host and pathogen microbiomes. Aphids host several species of heritable bacteria, some of which confer resistance against Pandora. We first found that spores that emerged from aphids that harbored protective bacteria were less virulent against subsequent hosts and did not grow on plate media. We then used 16S amplicon sequencing to study the bacterial microbiome of fungal mycelia and spores during plate culturing and host infection. We found that the bacterial community is remarkably stable in culture despite dramatic changes in pathogen virulence. Last, we used an experimentally transformed symbiont of aphids to show that Pandora can acquire host-associated bacteria during infection. Our results uncover new roles for bacteria in the dynamics of aphid-pathogen interactions and illustrate the importance of the broader microbiological context in studies of fungal pathogenesis.

IMPORTANCE

Entomopathogenic fungi play important roles in the population dynamics of many insect species. Understanding the factors shaping entomopathogen virulence is critical for agricultural management and for the use of fungi in pest biocontrol. We show that heritable bacteria in aphids, which confer protection to their hosts against fungal entomopathogens, influence virulence against subsequent hosts. Aphids reproduce asexually and are typically surrounded by genetically identical offspring, and thus these effects likely shape the dynamics of fungal disease in aphid populations. Furthermore, fungal entomopathogens are known to rapidly lose virulence in lab culture, complicating their laboratory use. We show that this phenomenon is not driven by changes in the associated bacterial microbiome. These results contribute to our broader understanding of the aphid model system and shed light on the biology of the Entomophthorales-an important but understudied group of fungi.

Potential for Use of Species in the Subfamily Erynioideae for Biological Control and Biotechnology

The fungal order Entomophthorales in the Zoopagomycota includes many fungal pathogens of arthropods. This review explores six genera in the subfamily Erynioideae within the family Entomophthoraceae, namely, Erynia, Furia, Orthomyces, Pandora, Strongwellsea, and Zoophthora. This is the largest subfamily in the Entomophthorales, including 126 described species. The species diversity, global distribution, and host range of this subfamily are summarized. Relatively few taxa are geographically widespread, and few have broad host ranges, which contrasts with many species with single reports from one location and one host species. The insect orders infected by the greatest numbers of species are the Diptera and Hemiptera. Across the subfamily, relatively few species have been cultivated in vitro, and those that have require more specialized media than many other fungi. Given their potential to attack arthropods and their position in the fungal evolutionary tree, we discuss which species might be adopted for biological control purposes or biotechnological innovations. Current challenges in the implementation of these species in biotechnology include the limited ability or difficulty in culturing many in vitro, a correlated paucity of genomic resources, and considerations regarding the host ranges of different species.