|MASCARIN, GABRIEL - Embrapa
|KOBORI, NILCE - Embrapa
|DELAIBERA, ITALO - Universidad De Sao Paulo
Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2015
Publication Date: 5/7/2015
Citation: Mascarin, G.M., Jackson, M.A., Kobori, N.N., Behle, R.W., Dunlap, C.A., Delaibera, I. 2015. Glucose concentration alters dissolved oxygen levels in liquid cultures of Beauveria bassiana and affects formation and bioefficacy of blastospores. Applied Microbiology and Biotechnology. 99(16):6653-6665. doi: 10.1007/s00253-015-6620-3.
Interpretive Summary: The insect-killing fungus Beauveria bassiana is one of the most widely used bioinsecticides in the world for control of numerous serious insect pests including bed bugs, aphids, whiteflies, and the coffee berry borer. Living spores of Beauveria are sprayed onto the insect pest, germinate and penetrate the insect, consume the nutrients within the insect, and kill the insect. Currently, spores of Beauveria are produced for commercial use by growing the fungus on moistened grains with spores being produced on the surface of the grains. This spore production process is very difficult to use on a large-scale, is labor intensive, and requires weeks for completion. We have optimized a method for producing spores of Beauveria using liquid culture fermentation. Our liquid fermentation method is very rapid (2-3 days), produces high concentrations of spores of Beauveria that can be dried and stored with excellent shelf-life, and results in living spores that are very effective in infecting and killing insects. Our production method for spores of Beauveria uses a low-cost diet coupled with high aeration rates and a high concentration of carbohydrate. Our liquid fermentation spore production method can be easily used on a commercial scale as it is the same method used to produce alcoholic beverages and pharmaceutical products. The development of this spore production process will facilitate the large-scale production of this important bioinsecticide and provide farmers, greenhouse operators, horticulturists, and home owners a valuable non-chemical insect control tool.
Technical Abstract: Beauveria bassiana is a ubiquitous dimorphic entomopathogenic fungus commonly used for controlling numerous insect pests worldwide. The goal of the present study was to optimize the production of B. bassiana to achieve high yields of the preferred morphology, a yeast-like blastospore, rather than mycelium. We examined the effects of oxygen level and glucose concentration on two strains of B. bassiana for culture growth, blastospore production, desiccation tolerance, and insecticidal activity. We demonstrated that high aeration (dissolved oxygen) rates in B. bassiana liquid cultures increased blastospore concentration (0.9–1.4 × 109 blastospores mL-1) and biomass (30.7–35.6 g L-1) in a short fermentation time of 2–3 days. Culturing B. bassiana in oxygen-rich media at a high initial glucose concentration (= 120 g L-1) yielded the highest number of blastospores within 3 days growth (1.1–3.3 × 109 cells mL-1). Furthermore, media amended with high glucose concentrations increased osmotic pressure which enhanced dissolved oxygen. Blastospores produced under these nutritional and environmental conditions were desiccation tolerant with a 55–70% survival rate when air dried to < 2.6% moisture. Blastospores of B. bassiana produced in media with high glucose concentrations (= 140 g L-1) were smaller in size with enhanced virulence against whitefly nymphs when compared with blastospores produced in media with a low-glucose (40 g L-1) concentration. Collectively, these results provide evidence of a synergistic effect between glucose concentration and oxygen availability on yeast-like growth by cultures of B. bassiana supporting superior yields of blastospores. These findings are significant for the development of cost-effective liquid culture production processes for infective, desiccation tolerant Beauveria blastospores, providing a catalyst for the adoption of blastospore-based bioinsecticides.