Heat shock proteins in the moderately halophilic bacterium deleya halophila: Protective effect of high salt concentration against thermal shock

The moderately halophilic eubacterium Deleya halophila grown in medium containing 1 M or 2.5 M NaCl was heat-shocked at various temperatures and the electrophoretic patterns of pulse-labelled proteins were examined. Several polypeptides were induced (heat shock proteins, or hsp) at all temperatures. However, the level of induction of some hsp was dependent on the severity of the thermal shock as well as the salt concentration of the growth medium. Time course studies revealed that synthesis of some of the hsp was transient when cells were grown in 1 M NaCl, while growth at 2.5 M NaCl resulted in the synthesis of most of the hsp at almost maximal level for at least 60 min following temperature shift-up. When cells were returned to normal growth temperature (30°C) after a heat shock treatment (47°C for 5 min), normal protein synthesis resumed faster when cells were grown in 1 M than in 2.5 M NaCl. During the recovery period, several major hsp appeared to be synthesized at near maximal level at both salt concentrations.