Responses of Gram-negative bacteria to certain environmental stressors.

Bacteria in nature are exposed to variations in temperature, and are affected by the availability of nutrients and water and the presence of toxic molecules. Their reactions to these changes require a series of rapid adaptive responses. Although transcriptional regulation is of primary importance in these responses, translational regulation and even activation of 'silenced' enzymes are critical for survival in changing environments. Bacteria have developed a series of mechanisms at the membrane structure level to cope with high concentrations of solvents. In addition, solvent-tolerant strains express highly effective efflux pumps to remove solvents from the cytoplasm. Desiccation tolerance is based on the synthesis and accumulation of osmoprotectants together with changes in fatty acid composition to preserve membrane structure. Both cold shock and heat shock responses are mainly regulated at a post-transcriptional level, translation efficiency in the case of cold shock and mRNA half-life and sigma32 stability in the case of heat shock.