Reproduction of Bacillus stearothermophilus as a Function of Temperature and Pressure

The colony-forming ability and the rate of reproduction of Bacillus stearothermophilus were determined as a function of temperature and pressure. Colonies were formed between 39 and 70 degrees C at atmospheric pressure and between 54 and 67 degrees C at 45 MPa. Colonies did not form at 55.9 MPa. The rate of reproduction in broth cultures decreased with increasing pressure at all temperatures. The rate of reproduction diminished rapidly with pressure above 10.4 MPa. Therefore, increased hydrostatic pressure was not sufficient to enable B. stearothermophilus to function beyond the temperature limiting growth and reproduction at atmospheric pressure, and B. stearothermophilus should grow in naturally or artificially warmed regions of the deep sea, where the pressure is less than approximately 50 MPa, although growth rates would be low above 10 MPa.