Electron Microscopy of the Altered Spore Morphology of a Ribonucleic Acid Polymerase Mutant of Bacillus Subtilis

Electron microscopy was used to analyze sporulating cells and spores of Bacillus subtilis mutants (Rif(r)) which are resistant to rifampin, an inhibitor of ribonucleic acid polymerase. The spores of Rif-18 are pleomorphic and frequently exhibit terminal knobs. These knobs first occur during late stage IV and early stage V of sporulation and are extensions of the inner and outer spore coats. Since the rifampin resistance and altered spore morphology of Rif-18 are 100% cotransformable, these data suggest that the altered spore morphology is the result of an alteration in ribonucleic acid polymerase genes. The morphology and physical dimensions are also reported for spores from Rif-11, Rif-15, and Rif-21. Significant differences in size from the wild type were observed for these mutants.