Bacterial Cold Shock Responses

Article excerpt

As a measure for molecular motion, temperature is one of the most important environmental factors for life as it directly influences structural and hence functional properties of cellular components. After a sudden increase in ambient temperature, which is termed heat shock, bacteria respond by expressing a specific set of genes whose protein products are designed to mainly cope with heat-induced alterations of protein conformation. This heat shock response comprises the expression of protein chaperones and proteases, and is under central control of an alternative sigma factor ([sigma].sup.32]) which acts as a master regulator that specifically directs RNA polymerase to transcribe from the heat shock promotors. In a similar manner, bacteria express a well-defined set of proteins after a rapid decrease in temperature, which is termed cold shock. This protein set, however, is different from that expressed under heat shock conditions and predominantly comprises proteins such as helicases, nucleases, and ribosome -associated components that directly or indirectly interact with the biological information molecules DNA and RNA. Interestingly, in contrast to the heat shock response, to date no cold-specific sigma factor has been identified. Rather, it appears that the cold shock response is organized as a complex stimulon in which post-transcriptional events play an important role. In this review, we present a summary of research results that have been acquired in recent years by examinations of bacterial cold shock responses. Important processes such as cold signal perception, membrane adaptation, and the modification of the translation apparatus are discussed together with many other cold-relevant aspects of bacterial physiology and first attempts are made to dissect the cold shock stimulon into less complex regulatory subunits. Special emphasis is placed on findings concerning the nucleic acid-binding cold shock proteins which play a fundamental role not only during cold shock adaptation but also under optimal growth conditions.

Sci. Prog. 86:9-75 [C] 2003 Science Reviews

Keywords: cold shock proteins, low temperature stress adaptation, membrane, pathogens, regulation, ribosome, temperature-dependent gene expression

Investigation of low temperature effects on bacteria -- what is it good for?

In recent years, the analysis of temperature-dependent gene expression at the molecular level has become of central importance to our understanding of several cellular functions. One of the aspects relevant in this context is bacterial pathogenicity. In many cases, the production of bacterial virulence factors required to successfully interact with and/or invade a host cell is temperature-controlled (1,2). Interestingly, it appears that pathogenic bacteria can be classified into two general groups depending on the direction of temperature change that triggers virulence factor expression. While human pathogens like Listeria and Yersinia or more generally speaking pathogens that selectively affect warm-blooded organisms usually experience an increase in ambient temperature upon contact with their host, many plant pathogens like Erwinia and Pseudomonas have been shown to activate virulence factor expression upon low temperature exposure thereby causing the typical "cold-weather" diseases (3). For example, it has been demonstrated that during nutrient deprivation P. syringae induces the production of INPs if exposed to cold shock (4). In contrast to AFPs that prevent or delay ice-crystal growth (5), INAs promote the formation of ice-crystals (6) and like AFPs have so far been identified in a number of organisms that have adapted to survive in cold environments, including bacteria (7,8). In case of P. syringae, INPs appear to induce frost damage in the leaves of the host plant resulting in the release of nutrients from the plant cell which thereafter can be utilized by the bacterium to promote growth.

It is clear that a detailed understanding of cold-induced molecular mechanisms employed by pathogens to negatively affect nutrient plants is of considerable public interest. …