28o SYNTHETIC CULTURE MEDIA 



Rivkin, and Rosenljerg' in nine groups, based upon the types of organisms for which 

 the media were designed. A review of the bacteriological Hterature up to 1925 shows 

 that approximately twenty-five hundred different combinations, which may be classi- 

 fied as synthetic media in the broader sense, have been described. It is manifestly 

 impossible here even to outline a classification of these media, and certainly im- 

 practicable to discuss formulas in detail. It is the purpose of this article briefly to 

 outline the newer knowledge relative to the uses to which synthetic media may be 

 put, and the precautions to be used in the development of a satisfactory or "op imum" 

 medium. 



Probably the outstanding advantage of a synthetic medium over a non-synthetic 

 medium is the ease of duplication. It is only when culture media are identical in 

 composition that the cultural characters of two organisms can be compared or the 

 results of studies by different observers on the same organism satisfactorily evaluated. 

 Synthetic media are essential in many cases to a determination of the exact nutrient 

 requirements of an organism, and often constitute the most satisfactory substrates 

 to be used in the isolation and identification of the various products of metabolism. 

 They lend themselves to the determination of ion effects or the necessity for the pres- 

 ence of bios, hormones, auximones, or other growth accelerants. In general, it is ad- 

 visable, when possible, to use synthetic media for studies of the chemical composition 

 of the cells of micro-organisms or of their products. Particular care is needed in testing 

 the purity of constituents when it is desired to determine the ability of organisms to 

 synthesize vitamines, bios, etc. 



A satisfactory synthetic medium should include: 



a) All elements essential to normal cell metabolism 



b) The elements combined into compounds which may be utilized by the cell 



c) Compounds which will act as buffers, poisers, etc., useful in that they tend to maintain a 

 suitable hydrogen-ion concentration, oxidation-reduction potential, etc. 



d) Compounds, elements, or ions not strictly nutrients but which may exert a stimulative 

 action 



e) All compounds and elements adjusted in concentration to give optimum growth conditions 



ELEMENTS ESSENTIAL FOR THE GROWTH OF MICRO-ORGANISMS 



The presence of an element, even in considerable amounts, in the cell of a micro- 

 organism is not sufficient to prove it essential. It has been repeatedly determined that 

 the chemical composition of the cell of a micro-organism may be markedly influenced 

 by the composition of the medium in which it is grown. Experimental evidence based 

 upon cultural tests is therefore necessary to determine the essential or the nonessen- 

 tial character of a particular element. 



Apparently all cells contain proteins, nucleo-proteins, and water. The elements 

 always found in these compounds, elements certainly essential to cell life, are carbon, 

 hydrogen, oxygen, nitrogen, phosphorus, and probably sulphur. In addition, potas- 

 sium, chlorine, and iron are generally regarded as necessary. It is common to in- 

 clude in the list sodium, calcium, and magnesium. It may be shown, however, that 

 with certain micro-organisms, at least the last-named elements are either nonessen- 

 tial or need to be present only in traces. 



' Krasnow, F., Rivkin, H., and Rosenberg, M. L.: J. Bad., 12, 385. 1926. 



