MICROMONOSPORIN, AN ANTIBIOTIC SUBSTANCE FROM A LITTLE-KNOWN GROUP OF MICROORGANISMS1

The genus Micromonospora belongs to one of the least-known genera of the Actinomycetales (Waksman and Henrici, 1943). It comprises both mesophilic and thermophilic forms and is found in soils, in manure and composts, in lake bottoms, and in other natural substrates. The micromonosporae are character-ized by the formation of single spores on side branches. Several species have now been recognized. In a survey of the distribution of antagonistic properties among the actinomy-cetes (Waksman, Horning, Welsch, and Woodruff, 1942), a strain of Micro-monospora was found to produce an antibiotic substance that was active against various gram-positive bacteria. This organism possessed rather interesting physiological properties. It grew in stationary liquid media or on solid media only to a very limited extent, producing an orange to brown slimy growth, with a smooth and shiny surface, which later turned brown or almost black. How-ever, in an aerated submerged condition, this organism grew very abundantly in the form of orange-colored compact clumps of "colonies " which nearly fille