Synthesis of mycotoxin protein IF8 by the entomopathogenic fungus Isaria fumosorosea and its toxic effect against adult Diaphorina citri.

Entomopathogenic fungi based microbial insecticides are considered as safe alternatives to chemical pesticides, which secretes several bioactive compounds to kill the host insects. In this study, we report a new approach for the synthesis and characterization of insecticide toxic protein IF8 produced by the Isaria fumosorosea 08, and to evaluate the mycotoxin level against the vector of Huanglongbing (HLB) or citrus greening disease, the Asian citrus psyllid, Diaphorina citri. Soluble toxic metabolites extracted from I. fumosorosea 08 through submerged liquid state culture had a molecular weight of 43 kDa when subjected by to sodium dodecyl sulfate-poly-acrylamide (SDS-PAGE) gel electrophoresis. The most abundant of toxic protein IF8 was determined by High-performance liquid chromatography (HPLC) and liquid chromatography electrospray ionization-mass spectroscopy (LC-ESI-MS) for the analysis of its molecular mass weight and purity. Further Matrix-assisted laser desorption ionization-time of flight (MALDI-TOFF) analysis confirmed the presence of toxic metabolites in liquid culture. Subsequently, mycotoxic effect of toxic protein IF8 was tested against D. citri at three different concentrations (1%, 2%, and 3%). The results showed the insecticidal activity of >80% when administered at three different concentrations at 48-120 hour post-application. Additionally, we also investigated the physicochemical properties and stability of IF8 by using computational biological tools. This is the first study to report the characterization of fungal mediated synthesis of the protein IF8 toxic to the insect D. citri. These results suggest the mycotoxin control of D. citri and prevention of HLB transmission by using a natural toxic compound which is eco-friendly and can be potentially used for the integrated management of D. citri.