A trans unsaturated fatty acid was found as a major constituent in the lipids of Pseudomonas putida P8. The fatty acid was identified as 9-trans-hexadecenoic acid by gas chromatography, argentation thin-layer chromatography, and infrared absorption spectrometry. Growing cells of P. putida P8 reacted to the presence of sublethal concentrations of phenol in the medium with changes in the fatty acid composition of the lipids, thereby increasing the degree of saturation. At phenol concentrations which completely inhibited the growth of P. putida, the cells were still able to increase the content of the trans unsaturated fatty acid and simultaneously to decrease the proportion of the corresponding 9-cis-hexadecenoic acid. This conversion of fatty acids was also induced by 4-chlorophenol in nongrowing cells in which the de novo synthesis of lipids had stopped, as shown by incorporation experiments with labeled acetate. The isomerization of the double bond in the presence of chloramphenicol indicates a constitutively operating enzyme system. The cis-to-trans modification of the fatty acids studied here apparently is a new way of adapting the membrane fluidity to the presence of phenols, thereby compensating for the elevation of membrane permeability induced by these toxic substances.

The physiological significance of trans unsaturated fatty acids, which are constituents of membrane lipids of the phenol-degrading bacterium Pseudomonas putita P8, was studied. The addition of phenol or phenol derivatives to the cells induced the formation of trans unsaturated fatty acids, yielding an overall maximal amount of 41.3°70 of total fatty acids. The inhibition of de-novo lipid synthesis by cerulenin prevented the change in the degree of saturation in the lipids. However, the cells could still respond to phenols with an amplified conversion of cis into trans unsaturated fatty acids, which is apparently a post-synthetic mechanism of isomerization of the double bond. The cis/trans conversion correlated with growth inhibition induced by toxic concentrations of 4-chlorophenol, whereas only growing cells were able to change the degree of saturation. In cells that were protected against phenol by immobilization in calcium alginate, the conversion of cis into trans fatty acids occurred at higher toxin concentrations compared with free ceils. Cells entering the stationary growth phase increased the proportion of saturated to unsaturated fatty acids but maintained a constant trans/cis ratio. P. putida P8 reacted to an increase or decrease in the growth temperature with an appropriate change in the ratio of saturated to unsaturated fatty acids and in ceils inhibited by cerulenin with a change in the trans/cis ratio. This study shows that the physiological role of the cis/trans conversion is probably the regulation of membrane fluidity when the most important mechanism for this, the modification of the degree of saturation, cannot be used by the cells due to inhibition of growth and lipid biosynthesis.

In the presence of sublethal concentrations of phenol, 4-chlorophenol, and p-cresol in the growth medium, cells of Escherichia coli modified the fatty acid composition of their lipids. The results of these changes was an increase in the degree of saturation of lipids probably in order to compensate an increase of fluidity of the membrane induced by the phenols. Supplementation of the growth medium with saturated fatty acids could also enhance the degree of lipid saturation due to the incorporation of the acyl chains in the phospholipids. At the same time the growth of cells was less inhibited than in unsupplemented cells. The increase of tolerance of cells by manipulating the lipid composition indicates that the membrane structure plays a crucial role in the mode of action of phenols.

The phospholipids of Pseudomonas putida P8 contain monounsaturated fatty acids in the cis and trans configuration. Cells of this phenol-degrading bacterium change the proportions of these isomers in response to the addition or elimination of a membrane active compound such as 4-chlorophenol. This study undoubtedly reveals that the cis unsaturated fatty acids are directly converted into trans isomers without involvement of de novo synthesis of fatty acids. Oleic acid, which cannot be synthesized by this bacterium, was incorporated as a cis unsaturated fatty acid marker in the membrane lipids of growing cells. The conversion of this fatty acid into the corresponding trans isomer was demonstrated by gas chromatographic-mass spectrometric analysis and use of 14C-labeled oleic acid. Separation and isolation of the cellular membranes showed that the fatty acid isomerase is located in the cytoplasmic membrane of P. putida P8.

A short time after the immobilization of Escherichia coli in calcium alginate substantial modifications of the fatty acid patterns of the cells were observed. This effect could be related to lipid impurities in the commercial alginate product used, which could be taken up, at least in part by the microorganisms. The impurities were mainly free fatty acids but sterols were also detected. Immobilization of the cells in alginate material extracted by chloroform or ethanol decreased the tolerance of the cells to phenol as compared with cells immobilized in raw alginate. This effect was diminished if the immobilized cells were exogenously supplied with palmitic acid, which is the main constituent of the fatty acids extracted from alginate. These results indicate that not only fatty acids but also other ingredients of commercial alginate have physiological effects on cells entrapped in this gel material.