Metabolomics reveals insect metabolic responses associated with fungal infection

Abstract

The interactions between insects and pathogenic fungi are complex. We employed metabolomic techniques to profile insect metabolic dynamics upon infection by the pathogenic fungus Beauveria bassiana. Silkworm larvae were infected with fungal spores and microscopic observations demonstrated that the exhaustion of insect hemocytes was coupled with fungal propagation in the insect body cavity. Metabolomic analyses revealed that fungal infection could significantly alter insect energy and nutrient metabolisms as well as the immune defense responses, including the upregulation of carbohydrates, amino acids, fatty acids, and lipids, but the downregulation of eicosanoids and amines. The insect antifeedant effect of the fungal infection was evident with the reduced level of maclurin (a component of mulberry leaves) in infected insects but elevated accumulations in control insects. Insecticidal and cytotoxic mycotoxins like oosporein and beauveriolides were also detected in insects at the later stages of infection. Taken together, the metabolomics data suggest that insect immune responses are energy-cost reactions and the strategies of nutrient deprivation, inhibition of host immune responses, and toxin production would be jointly employed by the fungus to kill insects. The data obtained in this study will facilitate future functional studies of genes and pathways associated with insect-fungus interactions.

Metabolic Conservation and Diversification of Metarhizium Species Correlate with Fungal Host-Specificity

“…The samples were centrifuged at a maximum speed for 10 min at 4°C, and the supernatants (75 μl each) were directly used for LC-MS analysis. Aliquots (75 μl each) of the supernatants were dried under nitrogen, derived using 200 μL methoxyamine (50 μg/ml in pyridine, 37°C for 16 h) and followed by the addition of 200 μL of N -methyl- N -trimethylsilyltrifluoroacetamide (J&K Scientific Company, Shanghai, China) at 37°C for 2 h. After centrifugation, the derived sample (1.0 μl) was injected splitlessly into a gas chromatography-mass spectrometry (GC-MS) system for analysis (Xu et al, 2015). …”

“…The drying gas and nebulizer nitrogen gas flow rates were set at 12 l/min and 30 psi. For full scan mode analysis, spectra were stored from m/z 50 to 1000 (Xu et al, 2015). …”

“…For LC-MS data, the features were temporarily identified based on accurate mass through matching databases: Combined Chemical Dictionary (version 8.1), Massbank, PubChem or METLIN. Furthermore, MS/MS information (fragment pattern) from different collision energies (low, medium, and high) was used to confirm the identified metabolites (Xu et al, 2015). …”

“…For example, metabolomic analyses of the insect pathogens M. brunneum and Beauveria bassiana cultured in different conditions revealed that both fungi produce significantly different arrays of secondary metabolites during infectious and saprophytic growths (de Bekker et al, 2013). Similarly, the chemical diversity of B. bassiana varied in association with the host and non-host growth cultures, and oxidative stress conditions (Luo et al, 2015; Xu et al, 2015; Zhang et al, 2016). The exploration of metabolomic technique could also help identify known metabolites that have not been reported in a given sample or organism.…”

“…For example, metabolomic analysis of B. bassiana mycelial samples identified the macrocyclic lactone, doramectin and a magnesium-containing antibiotic, magnesidin that were originally identified in bacteria (Luo et al, 2015). Our previous analysis of metabolic dynamics in silkworm ( Bombyx mori ) larvae identified a mulberry leaf component maclurin in insect hemolymph that reduced the feeding tendency of insects infected with B. bassiana , thus indicating an anti-feeding effect on insects infected with fungal pathogen (Xu et al, 2015). Metabolomic analysis has been also used to investigate and compare the intracellular metabolic responses among different yeast species (Christen and Sauer, 2011).…”