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Development of pilot-scale fermentation and stabilisation processes for the production of microsclerotia of the entomopathogenic fungus Metarhizium brunneum strain F52

Jackson, Mark A., Jaronski, Stefan T.
Biocontrol science and technology 2012 v.22 no.8 pp. 915
Metarhizium brunneum, biomass production, bioreactors, carbon nitrogen ratio, conidia, culture media, diatomaceous earth, drying, entomopathogenic fungi, fermentation, granules, growing media, sclerotia, strains
Using 100L stirred-tank bioreactors, we evaluated the effect of fermentation parameters and drying protocols on the production and stabilization of microsclerotia (MS) of the entomopathogenic fungus Metarhizium brunneum (formerly M. anisopliae F52). Results showed that stirred-tank bioreactors can be used to mass produce stable MS of Metarhizium and that culturing and drying protocols significantly affected MS yield and stability. Length of fermentation (4-7 days) for Metarhizium cultures had no significant impact on biomass accumulation, MS formation, or the storage stability of the air-dried MS granules. Although cultures of Metarhizium grown on media with a carbon-to-nitrogen (C:N) ratio of 30:1 produced significantly more biomass when compared to cultures grown in media with a C:N ratio of 50:1, MS formation and desiccation tolerance following drying were similar. After storage for 1 year at 4°C, conidia production by air-dried MS granules from 50:1 media was significantly higher compared to MS granules from 30:1 media. The addition of diatomaceous earth (DE) to cultures of Metarhizium prior to drying at rates of 0-60 g L-1 had no significant affect on MS desiccation tolerance but did impact conidia production. Air-dried MS granules without DE produced significantly more conidia g-1 during the first 4 months of storage, but after one year, conidia production was similar regardless of DE content of the MS granule. Microsclerotial granules with higher moisture levels (2.6-5.0% w/w) produced significantly more conidia immediately after drying and MS granules with low moisture (0-2.5% w/w) produced more conidia after 12 months storage.