P42: Use of real-time O2 concentration measurements in shake-flask fermentations of the bioinsecticidal fungus Isaria fumosorosea for improved yields of blastospores

The entomopathogenic fungus Isaria fumosoroseus (formerly Paecilomyces fumosoroseus) is capable of dimorphic growth (hyphal or yeast-like) in submerged culture. For use in spray applications as a biological control agent against insect pests, the yeast-like (blastospore) mode of growth is preferred. In shake-flask studies we evaluated the impact of aeration on the mode of growth of I. fumosorosea. Using 250 mL baffled, Erlenmeyer flasks, culture volumes of 50, 100, 150, and 200 mL of I. fumosorosea were grown in a shaker incubator at 350 rpm and 28 °C. Oxygen concentrations were continuously monitored using a non-invasive oxygen monitoring system. Results showed that culture volumes of 50 mL maintained O₂ concentrations above 15% saturation.  Fifty mL cultures accumulated biomass more rapidly and more than 80% of the biomass was blastospores. Culture volumes of 100-200 mL all showed O₂ depletion at some point during growth with lower blastospore yields and significantly more hyphal growth when compared to 50 mL cultures. Results from these studies were used to set oxygen concentration requirements (> 20% O₂ saturation) for I. fumosorosea growth in a 100 L bioreactor resulting in comparable results in terms of higher blastospore production with minimal hyphal growth.