Improvement of Thermotolerance of by Genes for Reactive Oxygen Species-Scavenging Enzymes and Heat Shock Proteins.

Thermotolerant genes, which are essential for survival at a high temperature, have been identified in three mesophilic microbes, including . Contrary to expectation, they include only a few genes for reactive oxygen species (ROS)-scavenging enzymes and heat shock proteins, which are assumed to play key roles at a critical high temperature (CHT) as an upper limit of survival. We thus examined the effects of increased expression of these genes on the cell growth of strains at its CHT. When overexpressed, most of the genes increased the CHT by about one degree, and some of them enhanced tolerance against acetic acid. These findings suggest that ROS-damaged molecules or unfolded proteins that prevent cell growth are accumulated in cells at the CHT.