[Selection of Streptomyces spheroides--a producer of extracellular proteases with fibrinolytic action].

The mutagenic action of UV on Streptomyces spheroides 35 spores produced mutants with an elevated biosynthesis of exocellular proteases having the fibrinolytic activity. During submerged cultivation, mutant M8-2 accumulated 4-5 times more fibrinolytic enzymes with a high thrombolytic activity in the cultural broth than the parent strain. The selection of mutants synthesizing proteases with a high fibrinolytic activity can be made more effective by using a medium which contains fibrin, a substrate specific for the enzymes, as a sole source of carbon and nitrogen. The diameters of zones of fibrin hydrolysis around the colonies on this medium are a reliable criterion in the selection of such mutants. The preparation of proteolytic enzymes isolated from the cultural broth of mutant M8-2 is 5.3 and 3.9 times more active in fibrin and casein hydrolysis, respectively, than the preparation of the parent strain. Moreover, it has a high thrombolytic activity.