Clues on the role of Beauveria bassiana catalases in alkane degradation events.

Entomopathogenic fungi adapt to growth in a culture medium containing an insect-like hydrocarbon as the sole carbon source inducing the beta-oxidation pathway during the alkane degradation. The effect of two carbon sources on the catalase activity was studied in the entomopathogenic fungus Beauveria bassiana. Catalase activity was detected both in the peroxisomal and cytosolic fraction. A significant increment in the specific activity of the peroxisomal fraction (12.6-fold) was observed when glucose was replaced by an insect-like hydrocarbon, whereas the specific activity in the cytosol diminished more than 1.2-fold in the same culture condition. After purification to homogeneity by gel filtration and strong anion exchange chromatography, an apparent molecular mass of 54.7 and 84.0 kDa per subunit were determined respectively for the peroxisomal and cytosolic catalase. The enzymes showed different biochemical and kinetic characteristics, but both were inhibited by 3-amino-1,2,4 triazole. Peroxisomal catalase was sensitive to pH, heat and high concentration of the hydrogen peroxide substrate. Inversely the cytosolic isoform exhibited a broad range of optimal pH (6.0-10.0), high thermostability (<55 C) and remained fully active at least up to 70 mM hydrogen peroxide. Measurement of catalase activity is a new approach for evaluating fungal ability to degrade hydrocarbons.