Cytotoxic activity in culture filtrates from the entomopathogenic fungus Beauveria sulfurescens

The hyphomycete fungus Beauveria sulfurescens secretes into the culture medium several components toxic for Galleria mellonella larvae. Concentrated and dialyzed (cutoff 12,000) B. sulfurescens culture filtrate also contains a highmolecular-weight compound cytotoxic for the Mamestra brassicae cell line. A fractionation in two chromatographic steps separated a cytotoxic fraction (IC(50)= 1.15 ± 0.05 μg/ ml), which was poorly toxic to larvae (LC(50) = 150 ± 10 μg/ ml) and an insecticidal fraction (LC(50) = 2.1 ± 0.1 μg/ml) devoid of detectable cytotoxicity. The two kinds of activity, i.e., cytotoxicity in vitroand toxicity in vivo are thus independent. The cytotoxic activity, initially detected on a M. brassicae cell line, also affected two other insect cell lines (G. mellonella and Spodoptera frugiperda). The cytotoxic fraction provoked not only the inhibition of cell proliferation, but also cell death. Adhesive mammalian cell lines were not sensitive. Nonadhesive mammalian cell lines of murine myeloma and hybridomas were poorly sensitive.