The cold shock response in the Gram-positive soil bacterium Bacillus subtilis is described. Cells were exposed to sudden decreases in temperature from their optimal growth temperature of 37 degrees C, The B. subtilis cells were cold shocked at 25 degrees C, 20 degrees C, 15 degrees C, and 10 degrees C. A total of 53 polypeptides were induced at the various cold shock temperatures and were revealed by two-dimensional gel electrophoresis. General stress proteins were identified by a comparative analysis with the heat shock response of B. subtilis. Some unique, prominent cold shock proteins such as the 115 kDa, 97 kDa, and 21 kDa polypeptides were microsequenced. Sequence comparison demonstrated that the 115-kDa protein had homology to the TCA cycle enzyme, aconitase.