Screening Methods in Microbiology 



THOMAS C. NELSON 



Eli Lilly and Company, Indianapolis, Indiana 



Screening methods as used in both basic and applied microbiology 

 are designed to uncover organisms possessing specific physiologi- 

 cal characteristics. The infrequent occurrence of these organisms, 

 existing as only a small fraction of the population, requires that an 

 effective screen be devised. Efficient screening techniques have been 

 developed for various types of organisms of interest in basic research. 

 Problems arise in adapting such techniques for industrial use, since 

 the aims of the two types of investigation are different. In basic 

 research the process and not the result is often of sole interest, the 

 yield of variant types being used as a measure of effectiveness of vari- 

 ables, as in studies on mutagenesis. When it is the variant organism 

 that is of interest, as in studies on the pathways of biosynthesis using 

 nutritionally deficient mutants, the property sought is a lack rather 

 than a gain of physiological function. Industrial screening searches 

 for a gain of function, either qualitative, in the production of a new 

 antibiotic, or quantitative, in yield improvement. Screens to detect 

 such changes, especially quantitative variations, are difficult to design. 

 It is however possible that some screening methods for readily 

 obtained variants can be adapted to industrial problems. This article 

 will discuss modifications of some screening methods of basic research 

 and the applicability of the resulting readily obtained variants to anti- 

 biotic production. Other industrial fermentations and aspects of 

 production are reviewed yearly (26). x 



Variants with Increased Yield 



The bulk of developmental microbiology in the antibiotics indus- 

 try consists in screening for increased yield, "potency" in industrial 

 jargon. More effort is expended in this phase of development than in 

 experimentation with media composition, conditions of fermenta- 

 tion, and purification. The reasons for this are, first, increase in vield 

 through culture selection has been continuous and usually larger in 



*See References, page 327. 



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