Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2013
Publication Date: 5/18/2013
Citation: Jackson, M.A. 2013. Dissolved oxygen levels affect microsclerotia formation by liquid cultures of metarhizium brunneum [abstract]. American Society for Microbiology. Poster 312. p. 113.
Technical Abstract: Sclerotia, overwintering propagules formed by some fungi when faced with adverse nutritional or environmental conditions, are composed of melanized hyphal aggregates capable of withstanding desiccation, oxidative stress, and UV radiation. Using liquid culture fermentation, we identified nutritional conditions that supported the formation of microsclerotia (small sclerotia) of the entomopathogenic fungus Metarhizium brunneum. Microsclerotia of M. brunneum show potential for use as a biocontrol agent for controlling soil-dwelling insect pests. In these studies, we examined the effect of dissolved oxygen (DO) on M. brunneum culture growth, microsclerotia formation, and microsclerotia melanization. Liquid cultures of M. brunneum were grown in a basal salts medium supplemented with glucose and acid hydrolyzed casein as carbon and nitrogen sources. In order to vary the DO concentration, 50, 100, 150, or 200 mL culture volumes were grown in 250 mL baffled Erlenmeyer flasks incubated at 350 rpm and 28 C in a rotary shaker incubator. Dissolved oxygen levels were continuously monitored using a non-invasive oxygen monitoring system. Dissolved oxygen levels for 50 mL culture volumes reached their lowest value, 9.7% DO, after 26.3 hours incubation while 200 mL cultures reached their lowest values of 2.0% DO in 11.5 hours. The DO values for culture volumes of 50 and 100 mL rose above 15% DO after 2 days growth while DO values for 150 and 200 mL cultures averaged 8.5% DO after 4 days growth. After 4 days growth, 50 and 100 mL cultures had similar dry weights (24.6 – 25.3 g/L) and microsclerotia concentrations (4.4 – 5.0 x 107 microsclerotia/L) that were significantly higher compared to 150 and 200 mL culture dry weights (15.3-17.6 g/L) and microsclerotia concentrations (1.7 – 2.4 x 107 microsclerotia/L). Melanization of microsclerotia was observed after 4 days growth in the 50 and 100 mL cultures but was never observed in the 150 and 200 mL cultures, even after culturing for 8 days. These results show that adequate aeration significantly increases microsclerotia formation and melanization by cultures of M. brunneum, information required for the scale-up of this fermentation process using stirred tank bioreactors.