Expression of a phenoloxidase cascade inhibitor enhances the virulence of the fungus Beauveria bassiana against the insect Helicoverpa armigera

Yang

Pest Management Science

et al. 2022

BACKGROUND: Metarhizium rileyi is an entomopathogenic fungus with promising potential for controlling agricultural pests, including Spodoptera frugiperda. Following penetration of the host through the cuticle, M. rileyi cells transform into in vivo blastospores or hyphal bodies, propagating within the hemocoel. However, the strategies and molecular mechanisms by which M. rileyi survives upon exposure to the powerful insect immune system remain unclear.RESULTS: We determined the pathogenicity of M. rileyi and found that either conidial immersion or blastospore injection significantly decreased S. frugiperda survival in a dose-dependent manner. Injection of M. rileyi blastospores decreased the number of S. frugiperda hemocytes and impaired host cellular reactions such as nodulation, encapsulation and phagocytosis. Blastospore injection led to increased antibacterial activity in plasma at 48 h post-injection (hpi). RNA-sequencing analyses identified a large number of antimicrobial peptide genes upregulated in the fat body of M. rileyi-infected larvae at 48 hpi, which may be attributable to the activation of Toll and IMD signaling pathway.CONCLUSION: This study demonstrates that the compromised cellular immunity of the insect host is due to the marked decrease in hemocytes and impaired cellular cytoskeletons, which may facilitate early infection by M. rileyi. Late in the course of infection, the enhanced antibacterial activity of plasma, which may be in response to intestinal evading bacteria, cannot inhibit hyphal growth in hemolymph. Our data provide a comprehensive resource for exploring the molecular mechanism employed by M. rileyi to overcome S. frugiperda immunity.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Infection of the entomopathogenic fungus Metarhizium rileyi suppresses cellular immunity and activates humoral antibacterial immunity of the host Spodoptera frugiperda

Yang

Pest Management Science

et al. 2022

“…It offers several advantages over traditional chemical pesticides, such as being eco-friendly, less harmful to nontarget organisms, and having a lower propensity for developing resistance ( 33 – 36 ). Researchers have been studying the possibility of using recombinant B. bassiana as a means of enhancing its efficacy against specific insect species ( 37 – 42 ). Genes-encoding insecticidal toxins derived from scorpions or bacteria have been introduced into B. bassiana to make it more lethal to mosquitoes ( 43 – 45 ).…”

Section: Discussionmentioning

confidence: 99%

Recombinant Beauveria bassiana expressing Bacillus thuringiensis toxin Cyt1Aa: a promising approach for enhancing Aedes mosquito control

Deng,

Li,

Yang

et al. 2024

Microbiol Spectr

The entomopathogenic fungus Beauveria bassiana provides an eco-friendly substitute to chemical insecticides for mosquito control. Nevertheless, its widespread application has been hindered by its comparatively slow efficacy in eliminating mosquitoes. To augment the potency of B. bassiana against Aedes mosquitoes, a novel recombinant strain, Bb -Cyt1Aa, was developed by incorporating the Bacillus thuringiensis toxin gene Cyt1Aa into B. bassiana . The virulence of Bb -Cyt1Aa was evaluated against Aedes aegypti and Aedes albopictus using insect bioassays. Compared to the wild-type (WT) strain, the median lethal time (LT 50 ) for A. aegypti larvae infected with Bb -Cyt1Aa decreased by 33.3% at a concentration of 1 × 10 8 conidia/mL and by 22.2% at 1 × 10 7 conidia/mL. The LT 50 for A. aegypti adults infected with Bb -Cyt1Aa through conidia ingestion was reduced by 37.5% at 1 × 10 8 conidia/mL and by 33.3% at 1 × 10 7 conidia/mL. Likewise, the LT 50 for A. aegypti adults infected with Bb -Cyt1Aa through cuticle contact decreased by 33.3% and 30.8% at the same concentrations, respectively. Furthermore, the Bb -Cyt1Aa strain also demonstrated increased toxicity against both larval and adult A. albopictus , when compared to the WT strain. In conclusion, our study demonstrated that the expression of B. thuringiensis toxin Cyt1Aa in B. bassiana enhanced its virulence against Aedes mosquitoes. This suggests that B. bassiana expressing Cyt1Aa has potential value for use in mosquito control. IMPORTANCE Beauveria bassiana is a naturally occurring fungus that can be utilized as a bioinsecticide against mosquitoes. Cyt1Aa is a delta-endotoxin protein produced by Bacillus thuringiensis that exhibits specific and potent insecticidal activity against mosquitoes. In our study, the expression of this toxin Cyt1Aa in B. bassiana enhances the virulence of B. bassiana against Aedes aegypti and Aedes albopictus , thereby increasing their effectiveness in killing mosquitoes. This novel strain can be used alongside chemical insecticides to reduce dependence on harmful chemicals, thereby minimizing negative impacts on the environment and human health. Additionally, the potential resistance of B. bassiana against mosquitoes in the future could be overcome by acquiring novel combinations of exogenous toxin genes. The presence of B. bassiana that expresses Cyt1Aa is of significant importance in mosquito control as it enhances genetic diversity, creates novel virulent strains, and contributes to the development of safer and more sustainable methods of mosquito control.

Pest Management Science

Expression of a viral ecdysteroid UDP‐glucosyltransferase enhanced the insecticidal activity of the insect pathogenic fungus Beauveria bassiana

Zhu,

Feng,

Liu

et al. 2024

BACKGROUNDEntomopathogenic fungi, such as Beauveria bassiana, hold promise as biological control agents against insect pests. However, the efficacy of these fungi can be hindered by insect immune responses. One strategy to enhance fungal virulence is to manipulate host immune by targeting key regulatory molecules like 20‐hydroxyecdysone (20E).RESULTSIn this study, we engineered B. bassiana strains to constitutively express the enzyme ecdysteroid UDP‐glucosyltransferase (EGT), which inactivates 20E, a crucial insect molting hormone. The engineered strain Bb::EGT‐1 exhibited robust expression of EGT, leading to a significant reduction in insect 20E levels upon infection. Moreover, infection with Bb::EGT‐1 resulted in accelerated larval mortality. Immune responses analysis revealed repression of insect immune response genes and decreased phenoloxidase (PO) activity in larvae infected with Bb::EGT‐1. Microbiome analysis indicated alterations in bacterial composition within infected insects, with increased abundance observed during infection with Bb::EGT‐1. Additionally, the presence of bacteria hindered hyphal emergence from insect cadavers, suggesting a role for microbial competition in fungal dissemination.CONCLUSIONSConstitutive expression of EGT in B. bassiana enhances fungal virulence by reducing insect 20E levels, suppressing immune responses, and altering the insect microbiome. These findings highlighted the potential of engineered fungi as effective biocontrol agents against insect pests and provide insights into the complex interactions between entomopathogenic fungi, their hosts, and associated microbes. © 2024 Society of Chemical Industry.