Biochemical Interaction between Entomopathogenous Fungi and Their Insect-Host-like Hydrocarbons

Abstract

The biochemical interaction between fungal pathogens and their insect host cuticle was studied by examining fungal hydrocarbon degrading activity, and the chain length of the lipid metabolites produced. Either n-octacosane or n-tetracosane substrate—of like chain length as the epicuticular straight chain hydrocarbons of Triatoma infestans—was used. Metarhizium anisopliae and Beauveria bassiana strains cultured on glucose-containing agar were able to degrade [3H] octacosane mainly into free fatty acids, phospholipids and acylglycerols. Volatile organic compounds (VOC) were also produced through β-oxidation reactions. When fungi were induced to grow on a hydrocarbon-enriched agar as the sole carbon source, hydrocarbon degrading activity was noticeably increased. The absence of very long chain fatty acids of like carbon skeleton as the supplemented hydrocarbon, i.e., the putative direct oxidation product, together with the large amounts of [3H] acetic acid produced, are supporting evidence for β-oxidation mechanisms going to completion, thus providing the acetyl-CoA units for de novo synthesis of fatty acids. Electron microscopy examination of 3,3'-diaminobenzidine-treated cells showed peroxisomal proliferation upon alkane-growth induction. These data provide the first insight on fatty acyl metabolites produced by fungal catabolism of insect-derived very long chain alkanes.