Gelatin as a Source of Growth-Promoting Substances for Bacteria.

In the course of studies on the nutritional requirements of some of the more exacting bacteria it wase found that the addition of certain brands of gelatin to a simplified synthetic medium caused growth of a number of bacteria which were unable to develop in the same medium without the gelatin. The use of gelatin in amounts ordinarily employed for culture media produced results which were comparable to, or at times better than, those secured by the use of small amounts of fractionated extracts of spleen, liver or yeast. Extracts of spleen, liver, yeast and other materials have been subjected by a number of workers to chemical fractionation in attempts to obtain growth-promoting substances responsible for development of the more fastidious bacteria. Since gelatin appeared to offer a promising source of these substances a further study of its effect was made. A comparison of results secured with the use of Difco gelatin and with a typical tissue preparation is given in table 1. The synthetic medium used in this experiment was similar in composition to that employed in previous work (Koser and Saunders, 1935) and contained inorganic salts, glucose, asparagin, cystine and tryptophane. None of the microorganisms were able to develop in the synthetic medium alone. The amounts of added spleen preparation and of gelatin necessary to secure development of five representative organisms are shown in the