Therefore, these differences in the phylogenetic diversities suggest that CTI is spread among all different groups of proteobacteria and the large identity variation indicates the enzymatic differences or development with the same enzymatic function (Heipieper et al. 2003). The next step was to verify the physiological activity of a cis–trans isomerase of unsaturated

fatty acids in M. capsulatus Bath. The most important environmental factors tested so far for their ability to trigger cis–trans isomerase activity in Pseudomonas and Vibrio strains are increases in temperature and the presence of organic solvents (Heipieper et al., 2003). Both factors are known to increase the fluidity Y-27632 mw of the membrane, which is discussed as being the major signal for an activation of the constitutively present CTI (Kiran et al., 2004, 2005). Therefore, in the first experiments, cells of M. capsulatus that were regularly grown at 45 °C were exposed to different temperatures and the effect on the fatty acid composition was measured. The membrane phospholipids of cells grown exponentially Selleckchem R428 at 45 °C contained the

following major fatty acids: C16:0, C16:1Δ9trans, C16:1Δ9cis, C16:1Δ10cis, C16:1Δ11cis and C17cyclo. This fatty acid pattern as well as the relative abundances of the fatty acids are in agreement with previous observations for this bacterium (Makula, 1978; Nichols et al., 1985; Bowman et al., 1991; Guckert et al., 1991). Table 2 summarizes the effect of different growth temperatures on the fatty acid composition of M. capsulatus. When the cells were exposed to 60 °C, a significant increase Depsipeptide in the trans/cis ratio of unsaturated fatty acids was observed within one hour, whereas no change occurred at the growth temperature of 45 °C or when the cells were exposed to a lower temperature of 30 °C (Fig. 1). This increase in the content of palmitelaidic acid (16:1transΔ9)

was caused by a decrease in the content of the corresponding isomer palmitoleic acid (16:1cisΔ9), whereas the abundance of the other forms of 16:1cis (16:1cisΔ10 and (16:1cisΔ11) that are known to be exclusively present in methanotrophic bacteria (Makula, 1978; Nichols et al., 1985; Bowman et al., 1991; Guckert et al., 1991) remained constant. This observation is in agreement with previous findings showing that double bonds located deeper in the phospholipid bilayer such as Δ10 or Δ11 cannot be converted by the cis–trans isomerase, which is a hydrophilic periplasmic protein. This enzyme can only reach double bonds at a certain depth in the membrane and could be ‘within reach’ of the active site of the enzyme, which is anchored at the membrane surface. Under the conditions tested, positions Δ10 and Δ11 would be ‘out of reach’ (Heipieper et al., 2001). These results provided an indication for the presence of a cis–trans isomerase of unsaturated fatty acids in M. capsulatus.