Hijacked: Co-option of host behavior by entomophthoralean fungi

Transcriptomic Profiling of Bean Aphid Megoura crassicauda upon Exposure to the Aphid-Obligate Entomopathogen Conidiobolus obscurus (Entomophthoromycotina) and Screening of CytCo-Binding Aphid Proteins through a Pull-Down Assay

Prolonged periods of host-lethal infection by entomopathogenic fungi pose challenges to the development of biological control agents. The obligate entomopathogen C. obscurus, however, rapidly kills aphid hosts, warranting investigation. This study investigated the interaction between C. obscurus and a bean aphid Megoura crassicauda during the incubation period of infection, using transcriptome analysis to map host gene expression profiles. Results indicate C. obscurus-inoculated aphid activation of the wound healing immune responses, alongside suppression of the key molecules involved in Toll signaling, melanization, and metabolism. Furthermore, neuromotor system-related genes were upregulated, paralleling the intoxication observed in a nematode pest treated with C. obscurus-derived CytCo protein. To deepen interaction insights, a His-tag pull-down assay coupled with mass spectrometry analysis was conducted using CytCo as a bait to screen for potential aphid protein interactors. The proteins were identified based on the assembled transcriptome, and eleven transmembrane proteins were predicted to bind to CytCo. Notably, a protein of putatively calcium-transporting ATPase stood out with the highest confidence. This suggests that CytCo plays a vital role in C. obscurus killing aphid hosts, implicating calcium imbalance. In conclusion, C. obscurus effectively inhibits aphid immunity and exhibits neurotoxic potential, expediting the infection process. This finding facilitates our understanding of the complex host-pathogen interactions and opens new avenues for exploring biological pest management strategies in agroforestry.

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.

Diversity and Breadth of Host Specificity among Arthropod Pathogens in the Entomophthoromycotina

A meta-analysis based on the published literature was conducted to evaluate the breadth of host ranges of arthropod pathogens in the fungal subphylum Entomophthoromycotina. The majority of pathogens in this subphylum infect insects, although arachnids (especially mites), collembola, and myriapods are also used as hosts. Most species (76%) have specialized host ranges and only infect arthropods in one host family. The breadth of host ranges in the Entomophthoromycotina is generally greater for species in more basal groups (Conidiobolaceae and Neoconidiobolaceae), where most species are soil-borne saprobes and few are pathogens. The Batkoaceae is a transitionary family in which all species are pathogens and both generalists and specialists occur. Among pathogen-infecting insects, Hemiptera and Diptera are the most commonly infected insect orders. Within the Hemiptera, hosts in the suborder Sternorrhycha were infected by more fungal species than the Auchenorrhyncha and Heteroptera.

Genomic Determinants of Entomopathogenic Fungi and Their Involvement in Pathogenesis

Entomopathogenic fungi offer an effective and eco-friendly alternative to curb insect populations in biocontrol strategy. The evolutionary history of selected entomopathogenic fungi indicates their ancestral relationship with plant endophytes. During this host shifting, entomopathogenic fungi must have acquired multiple mechanisms, including a combination of various biomolecules that make them distinguishable from other fungi. In this review, we focus on understanding various biochemical and molecular mechanisms involved in entomopathogenesis. In particular, we attempt to explain the indispensable role of enlarged gene families of various virulent factors, viz. chitinases, proteases, lipases, specialized metabolites, and cytochrome P450, in entomopathogenesis. Our analysis suggests that entomopathogenic fungi recruit a different set of gene products during the progression of pathogenesis. Knowledge of these bio-molecular interactions between fungi and insect hosts will allow researchers to execute pointed efforts towards the development of improved entomopathogenic fungal strains.

Evolution of zygomycete secretomes and the origins of terrestrial fungal ecologies

Fungi survive in diverse ecological niches by secreting proteins and other molecules into the environment to acquire food and interact with various biotic and abiotic stressors. Fungal secretome content is, therefore, believed to be tightly linked to fungal ecologies. We sampled 132 genomes from the early-diverging terrestrial fungal lineage zygomycetes (Mucoromycota and Zoopagomycota) and characterized their secretome composition. Our analyses revealed that phylogeny played an important role in shaping the secretome composition of zygomycete fungi with trophic mode contributing a smaller amount. Reconstruction of the evolution of secreted digestive enzymes revealed lineage-specific expansions, indicating that Mucoromycota and Zoopagomycota followed different trajectories early in their evolutionary history. We identified the presence of multiple pathogenicity-related proteins in the lineages known as saprotrophs, suggesting that either the ecologies of these fungi are incompletely known, and/or that these pathogenicity-related proteins have important functions associated with saprotrophic ecologies, both of which invite further investigation.

Genome-Wide Study of Conidiation-Related Genes in the Aphid-Obligate Fungal Pathogen Conidiobolus obscurus (Entomophthoromycotina)

Fungi in the Entomophthorales order can cause insect disease and epizootics in nature, contributing to biological pest control in agriculture and forestry. Most Entomophthorales have narrow host ranges, limited to the arthropod family level; however, rare genomic information about host-specific fungi has been reported. Conidiation is crucial for entomopathogenic fungi to explore insect resources owing to the important roles of conidia in the infection cycle, such as dispersal, adhesion, germination, and penetration into the host hemocoel. In this study, we analyzed the whole genome sequence of the aphid-obligate pathogen Conidiobolus obscurus strain ARSEF 7217 (Entomophthoromycotina), using Nanopore technology from Biomarker Technologies (Beijing, China). The genome size was 37.6 Mb, and encoded 10,262 predicted genes, wherein 21.3% genes were putatively associated to the pathogen–host interaction. In particular, the serine protease repertoire in C. obscurus exhibited expansions in the trypsin and subtilisin classes, which play vital roles in the fungus’ pathogenicity. Differentially expressed transcriptomic patterns were analyzed in three conidiation stages (pre-conidiation, emerging conidiation, and post-conidiation), and 2915 differentially expressed genes were found to be associated with the conidiation process. Furthermore, a weighted gene co-expression network analysis showed that 772 hub genes in conidiation are mainly involved in insect cuticular component degradation, cell wall/membrane biosynthesis, MAPK signaling pathway, and transcription regulation. Our findings of the genomic and transcriptomic features of C. obscurus help reveal the molecular mechanism of the Entomophthorales pathogenicity, which will contribute to improving fungal applications in pest control.

Mechanisms behind the Madness: How Do Zombie-Making Fungal Entomopathogens Affect Host Behavior To Increase Transmission?

Transmission is a crucial step in all pathogen life cycles. As such, certain species have evolved complex traits that increase their chances to find and invade new hosts. Fungal species that hijack insect behaviors are evident examples. Many of these "zombie-making" entomopathogens cause their hosts to exhibit heightened activity, seek out elevated positions, and display body postures that promote spore dispersal, all with specific circadian timing. Answering how fungal entomopathogens manipulate their hosts will increase our understanding of molecular aspects underlying fungus-insect interactions, pathogen-host coevolution, and the regulation of animal behavior. It may also lead to the discovery of novel bioactive compounds, given that the fungi involved have traditionally been understudied. This minireview summarizes and discusses recent work on zombie-making fungi of the orders Hypocreales and Entomophthorales that has resulted in hypotheses regarding the mechanisms that drive fungal manipulation of insect behavior. We discuss mechanical processes, host chemical signaling pathways, and fungal secreted effectors proposed to be involved in establishing pathogen-adaptive behaviors. Additionally, we touch on effectors' possible modes of action and how the convergent evolution of host manipulation could have given rise to the many parallels in observed behaviors across fungus-insect systems and beyond. However, the hypothesized mechanisms of behavior manipulation have yet to be proven. We, therefore, also suggest avenues of research that would move the field toward a more quantitative future.

Microbial Toxins in Insect and Nematode Pest Biocontrol

Invertebrate pests, such as insects and nematodes, not only cause or transmit human and livestock diseases but also impose serious crop losses by direct injury as well as vectoring pathogenic microbes. The damage is global but greater in developing countries, where human health and food security are more at risk. Although synthetic pesticides have been in use, biological control measures offer advantages via their biodegradability, environmental safety and precise targeting. This is amply demonstrated by the successful and widespread use of Bacillusthuringiensis to control mosquitos and many plant pests, the latter by the transgenic expression of insecticidal proteins from B. thuringiensis in crop plants. Here, I discuss the prospects of using bacterial and fungal toxins for pest control, including the molecular basis of their biocidal activity.

Long noncoding RNAs are potentially involved in the degeneration of virulence in an aphid-obligate pathogen, Conidiobolus obscurus (Entomophthoromycotina)

Virulence attenuation frequently occurs in in vitro culturing of pathogenic microbes. In this study, we investigated the total putative long noncoding RNAs (lncRNAs) in an aphid-obligate pathogen, Conidiobolus obscurus, and screened the differentially expressed (DE) lncRNAs and protein-coding genes involved in the virulence decline. The virulence was significantly attenuated after eight subculturing events, in which the median lethal concentration of the conidia ejected from mycelial mats relative to the bamboo aphid, Takecallis taiwanus, increased from 36.1 to 126.1 conidia mm^–2, four days after inoculation. In total, 1,252 lncRNAs were identified based on the genome-wide transcriptional analysis. By characterizing their molecular structures and expression patterns, we found that the lncRNAs possessed shorter transcripts, lower expression, and fewer exons than did protein-coding genes in C. obscurus. A total of 410 DE genes of 329 protein-coding genes and 81 lncRNAs were identified. The functional enrichment analysis showed the DE genes were enriched in peptidase activity, protein folding, autophagy, and metabolism. Moreover, target prediction analysis of the 81 lncRNAs revealed 3,111 cis-regulated and 23 trans-regulated mRNAs, while 121 DE lncRNA-mRNA pairs were possibly involved in virulence decline. Moreover, the DE lncRNA-regulated target genes mainly encoded small heat shock proteins, secretory proteins, transporters, autophagy proteins, and other stress response-related proteins. This implies that the decline in virulence regulated by lncRNAs was likely associated with the environmental stress response of C. obscurus. Hence, these findings can provide insights into the lncRNA molecules of Entomophthoromycotina, with regards to virulence regulators of entomopathogens.

Evolutionary relationships among Massospora spp. (Entomophthorales), obligate pathogens of cicadas

The fungal genus Massospora (Zoopagomycota: Entomophthorales) includes more than a dozen obligate, sexually transmissible pathogenic species that infect cicadas (Hemiptera) worldwide. At least two species are known to produce psychoactive compounds during infection, which has garnered considerable interest for this enigmatic genus. As with many Entomophthorales, the evolutionary relationships and host associations of Massospora spp. are not well understood. The acquisition of M. diceroproctae from Arizona, M. tettigatis from Chile, and M. platypediae from California and Colorado provided an opportunity to conduct molecular phylogenetic analyses and morphological studies to investigate whether these fungi represent a monophyletic group and delimit species boundaries. In a three-locus phylogenetic analysis including the D1-D2 domains of the nuclear 28S rRNA gene (28S), elongation factor 1 alpha-like (EFL), and beta-tubulin (BTUB), Massospora was resolved in a strongly supported monophyletic group containing four well-supported genealogically exclusive lineages, based on two of three methods of phylogenetic inference. There was incongruence among the single-gene trees: two methods of phylogenetic inference recovered trees with either the same topology as the three-gene concatenated tree (EFL) or a basal polytomy (28S, BTUB). Massospora levispora and M. platypediae isolates formed a single lineage in all analyses and are synonymized here as M. levispora. Massospora diceroproctae was sister to M. cicadina in all three single-gene trees and on an extremely long branch relative to the other Massospora, and even the outgroup taxa, which may reflect an accelerated rate of molecular evolution and/or incomplete taxon sampling. The results of the morphological study presented here indicate that spore measurements may not be phylogenetically or diagnostically informative. Despite recent advances in understanding the ecology of Massospora, much about its host range and diversity remains unexplored. The emerging phylogenetic framework can provide a foundation for exploring coevolutionary relationships with cicada hosts and the evolution of behavior-altering compounds.

Fungal artillery of zombie flies: infectious spore dispersal using a soft water cannon

Dead sporulating female fly cadavers infected by the house fly-pathogenic fungus Entomophthora muscae are attractive to healthy male flies, which by their physical inspection may mechanically trigger spore release and by their movement create whirlwind airflows that covers them in infectious conidia. The fungal artillery of E. muscae protrudes outward from the fly cadaver, and consists of a plethora of micrometric stalks that each uses a liquid-based turgor pressure build-up to eject a jet of protoplasm and the initially attached spore. The biophysical processes that regulate the release and range of spores, however, are unknown. To study the physics of ejection, we design a biomimetic 'soft cannon' that consists of a millimetric elastomeric barrel filled with fluid and plugged with a projectile. We precisely control the maximum pressure leading up to the ejection, and study the cannon efficiency as a function of its geometry and wall elasticity. In particular, we predict that ejection velocity decreases with spore size. The calculated flight trajectories under aerodynamic drag predict that the minimum spore size required to traverse a quiescent layer of a few millimetres around the fly cadaver is approximately 10 µm. This corroborates with the natural size of E. muscae conidia (approx. 27 µm) being large enough to traverse the boundary layer but small enough (less than 40 µm) to be lifted by air currents. Based on this understanding, we show how the fungal spores are able to reach a new host.

Pathogens of Dikerogammarus haemobaphes regulate host activity and survival, but also threaten native amphipod populations in the UK

Dikerogammarus haemobaphes is a non-native amphipod in UK freshwaters. Studies have identified this species as a low-impact invader in the UK, relative to its cousin Dikerogammarus villosus. It has been suggested that regulation by symbionts (such as Microsporidia) could explain this difference in impact. The effect of parasitism on D. haemobaphes is largely unknown. This was explored herein using 2 behavioural assays measuring activity and aggregation. First, D. haemobaphes were screened histologically post-assay, identifying 2 novel viruses (D. haemobaphes bi-facies-like virus [DhbflV], D. haemobaphes bacilliform virus [DhBV]), Cucumispora ornata (Microsporidia), Apicomplexa, and Digenea, which could alter host behaviour. DhBV infection burden increased host activity, and C. ornata infection reduced host activity. Second, native invertebrates were collected from the invasion site at Carlton Brook, UK, and tested for the presence of C. ornata. PCR screening identified that Gammarus pulex and other native invertebrates were positive for C. ornata. The host range of this parasite, and its impact on host survival, was additionally explored using D. haemobaphes, D. villosus, and G. pulex in a laboratory trial. D. haemobaphes and G. pulex became infected by C. ornata, which also lowered survival rate. D. villosus did not become infected. A PCR protocol for DhbflV was also applied to D. haemobaphes after the survival trial, associating this virus with decreased host survival. In conclusion, D. haemobaphes has a complex relationship with parasites in the UK environment. C. ornata likely regulates populations by decreasing host survival and activity, but despite this benefit, the parasite threatens susceptible native wildlife.

Zombie ant death grip due to hypercontracted mandibular muscles

There are numerous examples of parasites that manipulate the behavior of the hosts that they infect. One such host-pathogen relationship occurs between the 'zombie-ant fungus' Ophiocordyceps unilateralis sensu lato and its carpenter ant host. Infected ants climb to elevated locations and bite onto vegetation where they remain permanently affixed well after death. The mandibular muscles, but not the brain, of infected ants are extensively colonized by the fungus. We sought to investigate the mechanisms by which O. unilateralis s.l. may be able to influence mandibular muscle contraction despite widespread muscle damage. We found that infected muscles show evidence of hypercontraction. Despite the extensive colonization, both motor neurons and neuromuscular junctions appear to be maintained. Infection results in sarcolemmal damage, but this is not specific to the death grip. We found evidence of precise penetration of muscles by fungal structures and the presence of extracellular vesicle-like particles, both of which may contribute to mandibular hypercontraction.

Psychoactive plant- and mushroom-associated alkaloids from two behavior modifying cicada pathogens

Entomopathogenic fungi routinely kill their hosts before releasing infectious spores, but a few species keep insects alive while sporulating, which enhances dispersal. Transcriptomics- and metabolomics-based studies of entomopathogens with post-mortem dissemination from their parasitized hosts have unraveled infection processes and host responses. However, the mechanisms underlying active spore transmission by Entomophthoralean fungi in living insects remain elusive. Here we report the discovery, through metabolomics, of the plant-associated amphetamine, cathinone, in four Massospora cicadina-infected periodical cicada populations, and the mushroom-associated tryptamine, psilocybin, in annual cicadas infected with Massospora platypediae or Massospora levispora, which likely represent a single fungal species. The absence of some fungal enzymes necessary for cathinone and psilocybin biosynthesis along with the inability to detect intermediate metabolites or gene orthologs are consistent with possibly novel biosynthesis pathways in Massospora. The neurogenic activities of these compounds suggest the extended phenotype of Massospora that modifies cicada behavior to maximize dissemination is chemically-induced.

The Fungal Tree of Life: from Molecular Systematics to Genome-Scale Phylogenies

The kingdom Fungi is one of the more diverse clades of eukaryotes in terrestrial ecosystems, where they provide numerous ecological services ranging from decomposition of organic matter and nutrient cycling to beneficial and antagonistic associations with plants and animals. The evolutionary relationships of the kingdom have represented some of the more recalcitrant problems in systematics and phylogenetics. The advent of molecular phylogenetics, and more recently phylogenomics, has greatly advanced our understanding of the patterns and processes associated with fungal evolution, however. In this article, we review the major phyla, subphyla, and classes of the kingdom Fungi and provide brief summaries of ecologies, morphologies, and exemplar taxa. We also provide examples of how molecular phylogenetics and evolutionary genomics have advanced our understanding of fungal evolution within each of the phyla and some of the major classes. In the current classification we recognize 8 phyla, 12 subphyla, and 46 classes within the kingdom. The ancestor of fungi is inferred to be zoosporic, and zoosporic fungi comprise three lineages that are paraphyletic to the remainder of fungi. Fungi historically classified as zygomycetes do not form a monophyletic group and are paraphyletic to Ascomycota and Basidiomycota. Ascomycota and Basidiomycota are each monophyletic and collectively form the subkingdom Dikarya.

Entomopathogenic fungi and their potential for the management of Aedes aegypti (Diptera: Culicidae) in the Americas

Classical biological control has been used extensively for the management of exotic weeds and agricultural pests, but never for alien insect vectors of medical importance. This simple but elegant control strategy involves the introduction of coevolved natural enemies from the centre of origin of the target alien species. Aedes aegypti - the primary vector of the dengue, yellow fever and Zika flaviviruses - is just such an invasive alien in the Americas where it arrived accidentally from its West African home during the slave trade. Here, we introduce the concept of exploiting entomopathogenic fungi from Africa for the classical biological control of Ae. aegypti in the Americas. Fungal pathogens attacking arthropods are ubiquitous in tropical forests and are important components in the natural balance of arthropod populations. They can produce a range of specialised spore forms, as well as inducing a variety of bizarre behaviours in their hosts, in order to maximise infection. The fungal groups recorded as specialised pathogens of mosquito hosts worldwide are described and discussed. We opine that similar fungal pathogens will be found attacking and manipulating Ae. aegypti in African forests and that these could be employed for an economic, environmentally-safe and long-term solution to the flavivirus pandemics in the Americas.

A specialized fungal parasite (Massospora cicadina) hijacks the sexual signals of periodical cicadas (Hemiptera: Cicadidae: Magicicada)

Male periodical cicadas (Magicicada spp.) infected with conidiospore-producing (“Stage I”) infections of the entomopathogenic fungus Massospora cicadina exhibit precisely timed wing-flick signaling behavior normally seen only in sexually receptive female cicadas. Male wing-flicks attract copulation attempts from conspecific males in the chorus; close contact apparently spreads the infective conidiospores. In contrast, males with “Stage II” infections that produce resting spores that wait for the next cicada generation do not produce female-specific signals. We propose that these complex fungus-induced behavioral changes, which resemble apparently independently derived changes in other cicada-Massospora systems, represent a fungus “extended phenotype” that hijacks cicadas, turning them into vehicles for fungus transmission at the expense of the cicadas’ own interests.

Infection of Drosophila suzukii with the obligate insect-pathogenic fungus Entomophthora muscae

Physiological constraints restrict specialist pathogens from infecting new hosts. From an applied perspective, a narrow host range makes specialist pathogens interesting for targeting specific pest insects since they have minimal direct effects on non-target species. Entomopathogenic fungi of the genus Entomophthora are dipteran-specific but have not been investigated for their ability to infect the spotted wing drosophila (SWD; Drosophila suzukii) a fruit-damaging pest invasive to Europe and America. Our main goal was to study whether SWD is in the physiological host range of the entomophthoralean species E. muscae. We investigated pathogenicity and virulence of E. muscae towards its main natural host, the housefly Musca domestica, and towards SWD. We found that E. muscae readily infected and significantly reduced survival of SWD by 27.3% with the majority of flies dying 4-8 days post-exposure. In comparison with SWD, infection of the natural host M. domestica resulted in an even higher mortality of 62.9% and larger conidial spores of E. muscae, reflecting the physiological constraints of the pathogen in the atypical host. We demonstrated that pathogens of the E. muscae species complex that typically have a narrow natural host range of one or few dipteran species are able to infect SWD, and we described a new method for in vivo transmission and infection of an entomophthoralean fungus to SWD.