Chaetomin, a New Antibiotic Substance Produced by Chaetomium cochliodes

Abstract

Our knowledge of the production of antibiotic substances by fungi has been largely limited to the Hyphomycetes, especially the genera Penicillium and Aspergillus. Only very few members of the other groups of fungi were found capable of inhibiting the growth of microorganisms, including bacteria, through the production of such substances. In a survey of the distribution of antagonistic fungi in the soil (Waksman and Horning, 1943), over 160 cultures were isolated. Only one of these produced a perithecium, thus establishing its position among the Ascomycetes; this organism proved to be a species of Chaetomium, now identified as C. cochliodes. When grown on suitable media, this culture produced an antibiotic substance active principally against gram-positive bacteria. This substance is designated as chaetomin. FORMATION OF CHAETOMIN C. cochliodes does not sporulate readily when grown in synthetic media. However , on media containing peptone as a source of nitrogen, such as the glucose peptone agar, abundant dark green perithecia are produced, which later turn black. Czapek-Dox medium supplemented with a small amount of corn steep proved to be most suitable for the production of chaetonin, as table 1 shows. The addition of CaCO3 to the medium has an additional favorable effect upon the chaetomin formation, especially during the early stages of incubation of the cultures. This is of particular interest. since the organism apparently does not produce any acid, the reaction of the medium always tending to tum alkaline. The presence of CaCO3 was particularly favorable in submerged cultures, as table 2 brings out. Different carbohydrates, including brown sugar, lactose, and glucose, were tested as sources of energy for the growth of the organism and for the production of chaetomin. All were found to be about equally effective. In order to determine the nature of the essential factor present in the corn steep that is favorable for the production of chaetomin, a number of different plant juices were tested. Only one, the fresh juice of cabbage, could compare with corn steep, esecially for submerged cultures. These results, however, could not always be duplicated as was the case with corn steep; hence, the latter was always employed. A typical experiment illustrating the relation