A nonconventional two-stage fermentation system for the production of aerial conidia of entomopathogenic fungi utilizing surface tension.

AIM

To describe a new approach in which production of conidia of an entomopathogenic fungus takes place on the surface of an unstirred shallow liquid culture kept in nonabsorbent wells distributed in plastic sheets resembling a honeycomb.

METHODS AND RESULTS

First, liquid incubation time and medium composition for production of Beauveria bassiana aerial conidia were optimized. Wells inoculated with Sabouraud dextrose yeast extract produced 2·2 × 10 conidia per cm of liquid surface following 5 days of incubation. Finally, tests were carried out in a prototype comprised of stacked plastic sheets in a cylindrical container. Conidia production on liquid culture surface varied from 1·2 to 1·6 × 10 conidia per ml of fermented broth. Germination rates and insect activity towards Tenebrio molitor larvae were not negatively affected when compared to conidia produced on solid medium.

CONCLUSIONS

The two-stage fermentation process here described, based on a simple nonabsorbent inert support, has potential for the application in the production of aerial conidia of B. bassiana and other fungi.

SIGNIFICANCE AND IMPACT OF THE STUDY

Aerial conidia are the most extensive propagule type used in commercial mycopesticides, traditionally produced by solid-state fermentation (SSF). The industrial applications and other important benefits of the two-stage fermentation process here described may overcome some hurdles inherent to SSF aiming for the production of aerial conidia. Additionally, production consistency is increased by the use of chemically defined medium, and the better control of the environmental conditions could allow for more reproducible industrial batches.