cis/trans isomerization of unsaturated fatty acids as possible control mechanism of membrane fluidity inPseudomonas putida P8

Abstract

Exponentially growing cells of Pseudomonas putida had an increased ratio of saturated to unsaturated fatty acids in response to increased growth temperatures. Resting cells in which fatty acid biosynthesis was stopped reacted to a thermal increase by converting cis-monounsaturated fatty acids to trans isomers. cis/trans Isomerization of up to 60% of the unsaturated fatty acids was also activated by alcohols of different chain length. Their effective concentrations apparently depended on the lipophilic character of the alcohols. Also, a salt shock caused by the addition of NaCl resulted in the production of trans fatty acids. However, cells that were adapted to growth media of high osmolarity synthesized cyclopropane fatty acids instead of trans fatty acids. Activity of cis/trans-isomerase was dependent on the growth phase and was significantly higher during logarithmic growth than during the stationary phase. The results of this study agree with the hypothesis that the isomerization of cis into trans unsaturated fatty acids is an emergency action of cells of P. putida to adapt membrane fluidity to drastic changes of environmental conditions.

Formation of trans Fatty Acids Is Not Involved in Growth-Linked Membrane Adaptation of Pseudomonas putida

“…P. putida is known for possessing trans unsaturated fatty acids in its outer membrane. Surprisingly, and in contrast to earlier reports with the same strain, P. putida P8 (11,35), and related strains of P. putida (46,51), trans unsaturated fatty acids were not found in this study, regardless of the time of sampling. As shown in Table 1, trans fatty acids were not formed during exponential growth or stationary phase by any of the strains, provided that the cells were analyzed immediately after sampling.…”

“…At incubation temperatures that were lower than the cultivation temperature, no trans acids appeared (20 or 10°C). The strong temperature influence on the trans fatty acid formation is in accordance with earlier results (35). To verify our findings of the strong impact of sample treatment, we repeated some experiments that were done by other authors (22,24).…”

“…For 6 and 48 h of growth, S ranged from 47 to 52% and 50 to 54%, respectively. This increase with prolonged cultivation and depletion of the growth substrate confirms earlier data obtained with P. putida P8 (35) and resembles data obtained with chemostat cultures of Escherichia coli at different dilution rates (2,55). Increased contents of saturated fatty acids enhancing the rigidity of the cytoplasmic membrane are a well-known mechanism of adaptation to strong membrane-fluidizing factors such as a rise in temperature, growth on or in the presence of lipophilic organic solvents, etc.…”

“…Strains of this species are of ecophysiological interest because most of them are able to use at least the following three adaptation mechanisms at the level of lipids to respond to physical and chemical stresses: (i) changes in the overall degree of saturation of fatty acids (22,35,37), (ii) the formation of cyclopropane fatty acids (35), and (iii) cis-trans isomerization with a double bond configuration (11,22,35,36,37,46,59). The kind and degree of the response determine the stability and resilience of the cells and decide their fate.…”

Dynamics of a Pasture Soil Microbial Community after Deposition of Cattle Urine Amended with [ 13 C]Urea

“…In the HU treatment, however, such a reduction in CFA-to-precursor ratios was not observed despite the increase in PLFA yield (Table 2). Instead, a net production of CFAs occurred in the HU treatment, which could be interpreted as a stress response, since cyclopropane fatty acids have been shown to appear in microbial cell membranes in connection with various stresses, including hyperosmotic conditions (14,29). There is evidence that lipid extractability or partitioning during sample preparation increases with ionic strength (13), but the importance of this factor is not known.…”