Polyamines produced by an extreme thermophile are essential for cell growth at high temperature

An extreme thermophile, Thermus thermophilus grows at an optimum temperature of around 70 degrees C and produces 16 different polyamines including long-chain and branched-chain polyamines. We found that the composition of polyamines in the thermophile cells changes with culture temperature. Long-chain and branched-chain polyamines (unusual polyamines) were increased in the cells grown at high temperature such as 80 degrees C, but they were minor components in the cells grown at relatively lower temperature such as 60 degrees C. The effects of polyamines on cell growth were studied using T. thermophilus HB8 Delta speA deficient in arginine decarboxylase. Cell growth of this mutant strain was significantly decreased at 70 degrees C. This mutant strain cannot produce polyamines and grows poorly at 75 degrees C. It was also determined whether polyamines are directly involved in protecting DNA from DNA double-strand breaks (DSBs) induced by heat. Polyamines protected DNA against double-strand breaks. Therefore, polyamines play essential roles in cell growth at extremely high temperature through maintaining a functional conformation of DNA against DSBs and depurination.