Many antibiotics are produced as secondary metabolites of Streptomyces species. Commercial production of an antibiotic involves the optimization of environmental parameters, genetic makeup, and medium. Selection of ingredients for both inoculum (seed) and fermentation (production) media must provide for economic production, and easy downstream processing of the compound. Antibiotics are produced as secondary shunt metabolites and represent products that are not essential for primary metabolism of the cell; therefore conditions for their optimal expression may or may not be associated with good growth of the organism. Response Surface Methodology (RSM) is a collection of statistically designed experiments and analyses that directs the investigation of many factors and their interactions. This approach minimizes the number of trials required to identify critical factors and possible synergism between factors. In this research, an antifungal antibiotic produced by an unknown streptomycete collected from soil, was isolated, characterized and identified as cycloheximide. RSM was then used toformulate both a seed and production medium that optimizes cycloheximide biosynethesis. For the seed medium, RSM was used in a three step process: i) full factorial categorical screen of many factors, ii) Plackett-Burman two-level screen of promising factors, and iii) orthogonal central composite design of critical factors. Optimal 24 hour packed cell volume was found with a seed medium containing (g/L): 6.6g soluble starch, 23.4g yeast extract, and Mg K2HPO4. Additionally, the effects of inoculum age and passage on resulting cycloheximide production were studied. It was found that the negative effects of increasing inoculum age and passages on cycloheximide production could be mediated by the composition of the seed medium. For the production medium, RSM analysis of 29 ingredients suggests that an optimal production medium for cycloheximide biosynthesis should contain a combination of starch (40 g/L), corn gluten (17.8 g/L), MgSO4.7H2O (1.16 g/L), and NaCl (6.38 g/L). This final production medium resulted in a cycloheximide titer of 943 µg/ml, a 6-fold improvement in antibiotic production. / Department of Biology
| Identifer | oai:union.ndltd.org:BSU/oai:cardinalscholar.bsu.edu:handle/186964 |
| Date | January 2001 |
| Creators | Carter, William E. |
| Contributors | Mitchell, James K. |
| Source Sets | Ball State University |
| Detected Language | English |
| Format | vii, 116 leaves : ill. (some col.), charts ; 28 cm. |
| Source | Virtual Press |
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