Bacillus subtilis RUB1012 and RUB1013 have the following phenotype when grown at 45 degrees C: no growth on tryptose blood agar base, growth as clumps of spheres in broth culture, a slow autolysis rate, and a low proportion of teichoic acid to peptidoglycan. Revertants of strain RUB1012 (RUB2032, RUB2012, and RUB2042) that could grow on tryptose blood agar base were isolated. Each revertant had a different proportion of teichoic acid to peptidoglycan. The nanomoles of phosphorus per milligram of cell wall at the nonpermissive temperature were 141, 160, 236, and 541 for strain RUB1012 and revertants RUB2032, 2012, and 2042, respectively, as compared with 1,100 for the parent strain. With most bacteriophage tested, plating efficiency was related to the amount of glucosylated teichoic acid. Scanning electron microscopy was used to study strain RUB2032 during a shift from growth at 30 degrees C to growth at 45 degrees C. The change from rod to sphere began with the thickening of the cylindrical portion of the cell. Caps of the cells appeared to be immune to the thickening process. During growth, the cells became progressively shorter and thicker, and cell separation was inhibited. When cells of strain RUB2032 were shifted from growth at 45 degrees C to growth at 30 degrees C, accumulation of an amorphous material on the outer surfaces of the cells preceded the change from sphere to rod morphology. Cells remained clumped, with rods appearing at the periphery of the clumps. Analysis by DNA-mediated transformation and PBS1-mediated transduction indicated that strains RUB1012 and RUB1013 have multiple mutations mapping in the same region as other cell wall mutations.