Abstract
Thirteen thermosensitive mutants of Bacillus subtilis defective in the outgrowth phase of spore germination were isolated. The spores of the mutants grow into vegetative cells at 35 C but not at 47 C, whereas the vegetative cells grow equally well at both temperatures. At 47 C all the mutant spores are able to initiate germination, but the process stops at an early phase of outgrowth in one strain and in a late phase in the other 12 strains. The spore of the latter gives rise to a swollen cell unable to divide. In all mutants, the normal phenotype is restored when the spores are grown in the presence of 20% sucrose or 2% NaCl. The synthesis of deoxyribonucleic acid and proteins does not seem to be altered in the mutants giving swollen cells. The mutants were grouped into three distinct genetic classes by transformation.