Bacterial Temperature Adaptation by Molecular Chaperon GroE

Because temperature is one of the major factors influencing bacterial growth and survival, it is of considerable importance to understand how bacteria survive in their natural environment and how they adapt to temperatures outside of their normal growth range. In this respect, bacteria studied to date have been shown to acquire thermo-adaptation to normally lethal temperatures when pre-exposed to a milder, non-lethal heat shock. This phenomenon depends on heat shock proteins, especially the GroE chaperon, which supports the folding of polypeptides. The GroE chaperon consists of GroEL, a homotetradecameric double-ring cylinder composed of ~57 kDa subunits (1), and its co-chaperone GroES, a homoheptameric dome-shaped ring composed of ~10 kDa subunits. Both genes are essential for bacterial growth, and of the induction of GroE by heat shock prevents protein misfolding and aggregation. Therefore, we suspected that GroE plays a role in bacterial thermal adaptation. In the current report, we investigated temperature adaptation of Bacillus subtilis 168 in which the chromosomal groEL was replaced with a psychrophilic or mesophilic groEL gene. We found that temperature adaptation of this strain occurred by novel mutations in highly conserved regions of groEL.