Bacterial solvent responses and tolerance: cis–trans isomerization

The protocol describes the application of the membrane adaptive mechanism of Gram-negative bacteria belonging to the genera Pseudomonas and Vibrio, the isomerization of cis- to trans-unsaturated membrane fatty acids as a tool for the measurement of the toxicity of membrane-disturbing compounds. The degree of isomerization directly depends on the toxicity and concentration of membrane-affecting agents. Synthesis of trans fatty acids is apparent within 30 min after addition of stressors by direct isomerization of the respective cis configuration of the double bond without shifting the position. The purpose of the conversion of the cis configuration to trans is apparently a rapid decrease of the membrane fluidity to rising temperature or the presence of toxic organic hydrocarbons. Therefore, for those bacteria in which this mechanism is present, it offers the possibilities to use the trans/cis ratio of unsaturated fatty acids as an elegant, reliable, and rapid bioindicator for membrane stress in experimental setups.