Effect of fungal pellet size on the high yield production of destruxin B by Metarhizium anisopliae

Metarhizium anisopliae F061, a native Taiwan strain of an entomopathogenic fungus, was cultivated in the liquid-state fermentation. Three different types of fermentors with the optimal cultivation conditions could establish the high yield of destruxin B (DB), cyclodepsipeptide, a secondary metabolite of M. anisopliae. In 500 ml shaker-flasks, 336 mg l−1 of the DB was produced while the mean pellet size was 1.9 mm; in the 5 l stirred-tank, the pellet diameter was averaged to 2.1 mm, and the DB was 240 mg l−1; in the 20 l airlift reactor, DB yield could reach very high to 514 mg l−1, and the pellet size was found to be 1.8 mm. The larger or smaller pellet size gave poorer yield. It concluded that the most suitable size of the fungal pellet was found to be about 2.0 mm in diameter for M. anisopliae F061.