Bacillus subtilis mutant altered in spore morphology and in RNA polymerase activity.

A Bacillus subtilis mutant, that was selected for rifampin resistance produces spores with an altered morphology. The mutant spores are pleomorphic and differ both in shape and size from the wild-type spores. They frequently have an exosporium that is usually absent from wild-type spores. The mutant spores are similar to the wild-type spores in heat resistance, dipicolinic acid content, and density, but exhibit a slower rate of germination, outgrowth, and growth. In vitro studies show that the RNA polymerase of the mutant is resistant to rifampin inhibition, whereas the wild-type enzyme is completely inhibited by low concentrations of the antibiotic. Rifampin resistance and the altered spore morphology are contransformed with 100% frequency, suggesting that the altered morphology is caused by an alteration in the RNA polymerase.