In contrast, the transcriptomic analysis revealed a significant up-regulation of the cfa gene, which D-Pantothenic acid sodium encodes cyclopropane fatty acyl phospholipid synthase at time 80 and 310 min. The increase in cyclopropane fatty acid content in the cell membrane has previously been demonstrated to assist cells to maintain intracellular pH homeostasis by reducing membrane permeability to protons. This lipid modification provides protection against acid stress and other stress conditions such as high salt concentration and ethanol. Furthermore, our observations on fatty acid composition are consistent with the study of Guillot et al. on the response of Lactococcus lactis to osmotic stress, in which that organism was reported to increase the level of cyclopropane fatty acids, whereas the Estradiol Benzoate unsaturated-to-saturated fatty acids ratio remains unchanged. Several genes, encoding the key enzymes for lipopolysaccharide biosynthesis were down-regulated with a significant negative T-value at 80 and 310 min after hyperosmotic shift. The apparent reduction of lipopolysaccharide biosynthesis might indicate that outer membrane instability occurs during adaptation to hyperosmotic stress. Consistent with this, previous studies have reported that a defect in lipopolysaccharide biosynthesis leads to the lack of a continuous lipopolysaccharide layer in the outer membrane, causing increased susceptibility of bacterial cells to hydrophobic antibiotics. Furthermore, it has been demonstrated that the envelope stress caused by the defective biosynthesis of lipopolysaccharide increases the biosynthesis of the exopolysaccharide colanic acid. This, indeed, agrees well with earlier observations, indicating that the Rcs system-regulated colanic acid 
biosynthesis becomes activated. In response to hyperosmotic stress, E. coli increased expression of several genes and proteins involved in the Rcs phosphorelay system that regulates the biosynthesis of colanic acid. The T-profiler results revealed that a significant increase in overall expression of genes known to be induced by Rcs regulon occurred from 30 min of the osmotic treatment onward, whereas several Rcs-dependent proteins were significantly up-regulated only at the time point at which E. coli had resumed growth. These genes and proteins were also found to be amongst the most highly up-regulated in the present study. Consistent with these findings, Kocharunchitt et al. also demonstrated strong up-regulation of Rcs-dependent elements together with a high level of colanic acid production in E. coli cells during steady-state growth under a similar stress condition. The importance of colanic acid has frequently been described as protecting cells against a variety of stresses, including osmotic stress, and has been shown to be involved in biofilm formation. Although the physiological role of colanic acid is not well understood, it is thought that colanic acid expressed on cell surfaces simply provides a physical barrier to protect cells from hostile environments. Allen et al. has reported that colanic acid confers a strong negative charge to the cell surface. This negatively charged cell surface has led to the suggestion that colanic acid may help E. coli to maintain hydration of the cell surface, and to preserve the membrane lipids in the proper bilayer phase, as part of the adaptive strategies in response to such stress. However, the findings of Kocharunchitt et al. indicated that colanic acid is not required for growth and survival under osmotic stress.