Effect of restrictive temperature on cell wall synthesis in a temperature-sensitive mutant of Bacillus stearothermophilus

Abstract

A temperature-sensitive mutant of Bacillus stearothermophilus, TS-13, was unable to grow above 58 degrees C, compared to 72 degrees C for the wild type. Actively growing TS-13 cells lysed within 2 h when exposed to a restrictive temperature of 65 degrees C. Peptidoglycan synthesis stopped within 10 to 15 min postshift before a shut down of other macromolecular syntheses. Composition of preexisting peptidoglycan was not altered, nor was new peptidoglycan of aberrant composition formed. No significant difference in autolysin activity was observed between the mutant and the wild type at 65 degrees C. Protoplasts of TS-13 cells were able to synthesize cell wall material at 52 degress C, but not at 65 degrees C. This wall material remained closely associated with the cell membrane at the outer surface of the protoplasts, forming small, globular, membrane-bound structures which could be visualized by electron microscopy. These structures reacted with fluorescent antibody prepared against purified cell walls. Production of this membrane-associated wall material could be blocked by bacitracin, which inhibited cell wall synthesis at the level of transport through the membrane. The data were in agreement with previous studies showing that at the restrictive temperature this mutant is unable to alter its membrane fatty acid and phospholipid composition with temperature such that it is not able to maintain a membrane lipid composition which permits normal membrane function at the restrictive temperature.