N-Acetyl-d-Glucosamine-Mediated Regulation of Extracellular Protease in the Entomopathogenic Fungus Beauveria bassiana

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The entomopathogenic fungus Beauveria bassiana GK2016 grown in a liquid medium incorporating gelatin as the sole carbon and nitrogen source produced an extracellular serine protease (molecular weight, 35,000; pI ca. 10). Without gelatin, B. bassiana could utilize N-acetyl-d-glucosamine (GlcNAc; 2-acetamido-2-deoxy-d-glucose) as the sole source of carbon and nitrogen, and GlcNAc availability increased the storage carbohydrate content in mycelia. Synthesis of protease was repressed in gelatin medium containing GlcNAc at levels of >1.07 μmol mg of fungal dry weight−1. At levels below this, protease synthesis was initiated; subsequently, free amino nitrogen appeared in the medium and diauxic growth was observed. Slow feeding with GlcNAc (35.34 μg ml−1 h−1) did not repress protease synthesis nor did GlcNAc accumulate in the medium above 0.5 mg ml−1. Increasing the rate of release of GlcNAc (83.51 μg ml−1 h−1) resulted in the accumulation of GlcNAc in the medium to 2.0 mg ml−1, a 45% increase in growth and a decrease in protease synthesis by about 81%. Free amino acids generated from the hydrolysis of gelatin did not repress protease synthesis. These data are interpreted in terms of known interaction of B. bassiana with insect cuticular components. We suggest that the action of extracellular chitinases synthesized by B. bassiana on insect cuticle, and pursuant release of GlcNAc, may have important consequences on the regulation of other extracellular catabolic enzymes such as the protease.

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