[A statistical method for the determination of the yield correlation of antibiotic-producing microorganisms].
The antibiotic yields of industrial selectants must be checked at several steps of cultivation. Here the question arises whether the activities at the different levels of cultivation are correlated. The common coefficient of correlation cannot be used because repeated determinations of the yield at one selectant result in different values. In order to have only one fixed value per selectant we define the mean value around which the observed values are varying. But these mean values cannot be observed. Thus, an adequate method of correlation similar to that in Guiard and Herrendörfer (1977) was used. The method is demonstrated in two examples: With selectants of Streptomyces noursei for streptothricin titers in 20 ml- and 20 l-cultures as well as with selectants of Penicillium chrysogenum for potency indices in surface cultures and penicillin titers in 50 ml submerged cultures, respectively. In both cases the coefficients of correlation were above 0.7.
Development and evaluation of a potency index screen for detecting mutants of Penicillium chrysogenum having increased penicillin yield.
U.v.-treated conidia of an industrial strain of Penicillium chrysogenum were spread on a growth-limiting agar medium. Colonies arising from the survivors were surrounded with a spore suspension of Bacillus subtilis to which penicillinase had been added. After appropriate incubation, discrete zones of bacterial inhibition, with sizes limited by the penicillinase, appeared around each colony. Using the criterion of potency index (diameter of inhibition zone divided by diameter of colony) strains were selected that subsequently gave improved penicillin production in shake-flasks. The technique also ranked correctly four industrial strains in order of their known penicillin-producing capacity. Employing three operators, 5000 isolates could be screened in each experiment and approx. 15000 strains could be screened in a month.
The design of fermentation and biological assay procedures for assessment of penicillin production in populations of Aspergillus nidulans.
The design of shake flask fermentations and biological assay procedures for the assessment of penicillin titres in populations of Aspergillus nidulans strains is described. Consideration of the amount and stage of replication and the arrangement of the culture filtrates on the assay plate led to the adoption of a general procedure where strains are replicated in 2, 3 or 4 flasks, depending upon the precision required. Each flask is tested using only one inhibition zone and the zones for one replicate set of strains are completely randomized on one assay plate. This experimental design does not require a high degree of statistical competence for interpretation of the results and it may be easily adapted to accommodate a variety of experimental sizes or to allow any required level of discrimination between strains to be achieved. The general approach and principles may be applied to many large scale, low precision assays carried out in fermentation research.