DNA supercoiling and thermal regulation of unsaturated fatty acid synthesis in Bacillus subtilis.

Bacillus subtilis growing at 37 degrees C synthesizes, almost exclusively, saturated fatty acids. However, when a culture growing at 37 degrees C is transferred to 20 degrees C, the synthesis of unsaturated fatty acids is induced. The addition of the DNA gyrase inhibitor novobiocin specifically prevented the induction of unsaturated fatty acid synthesis at 20 degrees C. Furthermore, it was determined that plasmid DNA isolated from cells growing at 20 degrees C was significantly more negatively supercoiled than the equivalent DNA isolated from cells growing at 37 degrees C. The overall results agree with the hypothesis that an increase in DNA supercoiling associated with a temperature downshift could regulate the unsaturated fatty acids synthesis in B. subtilis.