[Thermosensitive sporulation and extracellular serylprotease mutant of B. subtilis]

Isolation and properties of B. subtilis ts 19 mutant, isolated as thermosensitive for sporulation, are described. At the non permissive temperature (42degreesC), the mutant cells are blocked at stage zero of sporulation and do not excrete extracellular enzymes such as serylprotease and esterase. At the permissive temperature (30degreesC), sporulation and excretion of extracellular enzymes are normal but the serylprotease is modified in its structure. Two molecular forms of this enzyme can be separated by polyacrylamide elecctrophoresis, both more thermolabile than the corresponding enzyme of the mother strain. Experiments of reversion and of transformation for the sporulation character have suggested that ts 19 contained two independent thermosensitive mutations. One of them is responsible for the pleiotropic Spo OA phenotype at the non permissive temperature. The other mutation is likely to reside in the structural gene coding for the extracellular serylprotease and leads to the formation of a modified enzyme which hydrolyzes itself into at least two types of more stable molecules. No conclusion can be drawn with certainty concerning the physiologi-al role of the extracellular serylprotease in sporulation. It may be pointed out however that transformants for the Sp+ character at 42degreesC keep the same impaired serylprotease as the ts 19 mutant and sporulate, at any temperature, as well as the wild strain.