Development of entomopathogenic fungi in mosquito control: which kind of production for which efficiency?

Abstract

Mosquitoes (Diptera: Culicidae) are zoonotic vectors responsible for numerous infectious diseases of medical and veterinary importance such as filariasis, malaria and encephalitis. As part of an integrated vector control, entomopathogenic fungi could be developed as biopesticides in two ways: spores and metabolites recognized as effective virulence factors. Solid-state fermentation enhances spore production and induces the secretion of metabolites quantitatively and qualitatively different from submerged fermentation, which impairs fungal metabolic efficiency. In this context, we showed high spore productivity of solid-state media based on agro-industrial substrates as wheat bran. Spores remained pathogenic, as revealed by classical toxicity tests and electron microscopy. However, the absence of free water makes culture parameter variations difficult to control in large-scale. Recently, we performed a bioreactor design intended for simultaneous spore and metabolite production, combining the technological advantages of submerged and solid-state fermentations. Biofilm fermentation (i.e. growth of fungal biomass on an inert support immerged in a nutrient medium) is a tremendous production system favouring the secretion of insecticidal metabolites in the liquid medium as we showed recently. This is also an interesting tool to provide an overview of the complexity of the metabolic pathways involved in the regulation of extracellular metabolites secretion because corresponding genes are reported to be differentially expressed from classical fermentation systems. Researches in vector control are currently intensified. In this context, the identification of genes and metabolites specifically expressed during biofilm fermentation will help to develop new technologies related both to the design of bioreactor and the production of insecticidal proteins