Improvement of medium composition by random balance designs

If the number of potentially relevant compounds which have to be optimally selected is large, then random balance experimentation provides a useful tool for the development of nutrient media. The object of investigation was a thiostrepton producing Streptomyces strain from our own collection. The thiostreptone formation was increased although we had insufficient information about the physiological needs or regulation aspects concerning the biosynthesis. The medium development was carried out alongside mutation experiments within a limited temporal interval. Our study shows how a 9‐component medium can be improved by a 6‐point experimental design. At the end of the paper the basic principles for constructing restricted random balance designs are outlined.