Development of high heat resistance of Arizona neotype by preincubation at 35 degrees C in media containing NaCl.

When cells of Arizona neotype were preincubated at 35 degrees C in a medium containing NaCl (1 to 10%), they were found to be much more heat resistant upon being tested at 57 degrees C in a Trypticase (BBL Microbiology Systems) soy-yeast extract broth medium containing 10% NaCl than cells that had not been preincubated. Although no growth takes place during preincubation in the presence of 10% NaCl, some metabolic activity is necessary, since the presence of 2,4-dinitrophenol during incubation reduced the amount of gain in heat resistance. Incubation in the presence of N2, instead of air, abolished the effect. Chloramphenicol and rifampin, however, had no effect. Preincubated cells were just as heat resistant when separated by centrifugation and suspended in a fresh medium as when suspended in the incubated supernatant liquid. Conversely, the incubated supernatant liquid did not confer increased heat resistance upon unincubated cells. The increase in heat resistance, therefore, is probably a result of the salt osmotically plasmolyzing the cells by removing intracellular water, thus rendering the cellular contents more stable to heat. It is not known, however, why metabolic activity is necessary.