ENHANCED THERMOTOLERANCE AND TEMPERATURE-INDUCED CHANGES IN PROTEIN-COMPOSITION IN THE HYPERTHERMOPHILIC ARCHAEON ES4

The hyperthermophilic archaeon ES4, a heterotrophic sulfur reducer iso lated from a deep-sea hydrothermal vent, is capable of protecting itse lf from thermal stress at temperatures above its optimum for growth. T he thermotolerance of ES4 was determined by exposing log-phase cells t o various lethal high temperatures. When ES4 was shifted from 95 to 10 2-degrees-C, it displayed recovery from an exponential rate of death, followed by transient thermotolerance. When ES4 was shifted directly f rom 95 to either 105 or 108-degrees-C, only exponential death occurred . However, a shift from 95 to 105-degrees-C with an intermediate incub ation at 102-degrees-C also gave ES4 transient thermotolerance to 105- degrees-C. The protein composition of ES4 was examined at temperatures ranging from 75 to 102-degrees-C by one-dimensional electrophoresis. Two proteins with molecular masses of approximately 90 and 150 kDa sig nificantly decreased in abundance with increasing growth temperature, while a 98-kDa protein, present at very low levels at normal growth te mperatures (76 to 99-degrees-C), was more abundant at higher temperatu res. The enhanced tolerance to hyperthermal conditions after a mild hy perthermal exposure and the increased abundance of the 98-kDa protein at above-optimal temperatures imply that ES4 is capable of a heat shoc k-like response previously unseen in hyperthermophilic archaea.