Lxxvi. Indole Formation by Bacterium Coli

KuHNE [1875] recognised indole as one of the products of the bacterial decomposition of proteins. The discovery of tryptophan by Hopkins and Cole [1901] was followed by the proof by these authors that tryptophan was the parent substance of bacterially formed indole [Hopkins and Cole, 1903]. They succeeded in isolating indole and indoleacetic acid from the products of the aerobic growth of bacteria (including Bact. coli) on a medium consisting of pure tryptophan and gelatin. Under anaerobic conditions they were able to isolate indolepropionic acid. Hertzfeldt and Klinger [1915] studied, in roughly quantitative manner, the relationship between the disappearance of tryptophan and the production of indole with both indole-positive and indole-negative organisms. They used peptone medium and also a medium of pure tryptophan and salts, in which tryptophan was the sole source of nitrogen. In the latter case it is noteworthy that a form of bacterial suspension was used. Raistrick and Clarke [1921] investigated the bacterial decomposition of both the side chain and ring of tryptophan, but Bact. coli was not used. Fellers and Clough [1925] made a careful survey of the tests available for the detection of indole and skatole in bacterial cultures and applied them to a large number of bacterial species, but peptone and similar complex media were employed. Bact. coli was chosen for the following work since it is a strongly indolepositive organism. An additional advantage is that Bact. coli does not decompose indole [Hertzfeldt and Klinger, 1915].