P75: The impact of culture age, aeration, and agitation on the production of microsclerotia of the entomopathogenic fungus Metarhizium anisopliae

Microsclerotia are desiccation-tolerant, compact hyphal aggregates produced by numerous fungi as overwintering structures.  We recently discovered that the entomopathogenic fungus Metarhizium anisopliae produced microsclerotia during liquid culture fermentation. When air-dried microsclerotial granules of M. anisopliae were soil incorporated, they germinated upon rehydration to produce conidia that infected and killed soil-dwelling insects. The production of microsclerotial forms of M. anisopliae using liquid fermentation provides impetus for their commercial use as a bioinsecticide. In this study, M. anisopliae cultures were grown in 100L fermentors using various agitation and aeration rates. Microsclerotia were harvested at various culture times, mixed with diatomaceous earth, de-watered, and air-dried to less than 4% moisture.  Air-dried microsclerotial granules derived from cultures 4 to 7 days old showed no significant differences in viability (all granules greater than 90% hyphal germination) or conidia production (3.8 – 5.7 x 10¹⁰ conidia L^-1 fermentation broth). Storage of these air-dried microsclerotial preparations for 12 months at 4 ºC resulted in no significant loss in viability or conidia production regardless of culture age. While aeration rates (20-60 SLPM) had no significant impact on conidia production potential for air-dried microsclerotial preparations, lower agitation rates (150–200 rpm) yielded microsclerotial preparations that produced more conidia compared to cultures grown with higher agitation rates (300-420 rpm). These results show that microsclerotia of M. anisopliae can be produced using deep-tank fermentation and that higher agitation rates during cultivation may negatively impact microsclerotia formation, function, or stability.