Cellular Response to Heat Shock and Cold Shock

Abstract

This chapter reviews the molecular response of bacteria to shifts in either high or low temperatures. It discusses the inputs to each response, the outputs needed to cope with the sudden stress, and the molecular circuitry that controls these stress responses, and reviews the strategies utilized to cope with sudden heat stress or cold shock by mesophilic bacteria, focusing on Escherichia coli, the most completely studied bacterial species. The chapter talks about the relationship between temperature and the steady-state growth rate for this organism, and considers how E. coli responds to shift to both high and low temperatures, with a goal of integrating our knowledge about each response. Although the focus is on E. coli, the strategies used by E. coli with those used by Bacillus subtilis, are compared. When cells are shifted within the normal growth range, there is little or no lag in adaptation to the new growth rate and neither a heat shock response (HSR) nor a cold shock response (CSR) is elicited. The demonstration that overproduction of a variety of unfolded proteins triggers the HSR without temperature shift solidified the idea that such molecules serve as a signal controlling the response. Molecular understanding of this signaling mechanism is described in the circuitry section. RhlB is present during cold shock and it is not clear whether degradosomes contain both helicases or whether different populations of degradosomes contain one or the other. More DnaK is associated with the degradosome during cold shock.