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Oosporein, an abundant metabolite in Beauveria caledonica, with a feedback induction mechanism and a role in insect virulence

Mc Namara, Louise, Dolan, Stephen K., Walsh, John M.D., Stephens, John C., Glare, Travis R., Kavanagh, Kevin, Griffin, Christine T.
Fungal biology 2019 v.123 no.8 pp. 601-610
Beauveria bassiana, Galleria mellonella, Hylobius abietis, adults, antifeedants, biological control agents, biosynthesis, enzymes, forestry, hemocytes, immune system, immunomodulation, insect larvae, insects, metabolites, pests, proteomics, virulence
Oosporein was first identified from the insect pathogen Beauveria bassiana >50 y ago. Here, we investigate the insecticidal, anti-feedant and immunomodulation effects of oosporein produced by Beauveria caledonica on the forestry pest Hylobius abietis and model insect Galleria mellonella. We report a novel feedback induction mechanism regulating oosporein production in B. caledonica; exogenous oosporein induces the expression of the oosporein cluster, leading to increased abundance of oosporein biosynthetic enzymes, as shown by label-free quantitative proteomics. Oosporein did not have an anti-feedant effect on H. abietis adults – on the contrary, insects exposed to oosporein-treated food fed more than those exposed to untreated food only. Injected oosporein did not kill insect larvae but increased susceptibility of H. abietis to a subsequent infection. Oosporein did not act as a contact toxin on H. abietis adults and G. mellonella larvae at the concentrations tested. Therefore, it appears that oosporein promotes infection rather than directly killing insects; this could be mediated both by a reduction in haemocyte numbers and by alterations to the humoral immune system. This work makes a case for future research into the potential use of B. caledonica as a biocontrol agent through combinations with oosporein or with enhanced production of oosporein.