A rather efficient solvent adaptation mechanism enabling several gram-negative bacteria to tolerate and grow in the presence of membrane-disturbing compounds is the isomerization of cis- to trans-unsaturated membrane fatty acids. The degree of isomerization obviously depends on the toxicity and the concentration of membrane-affecting agents. Synthesis of trans-fatty acids comes about 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 the rapid adaptation of the membrane fluidity to rising temperature or the presence of toxic organic hydrocarbons.

The cis–trans-isomerase (Cti) is a constitutively expressed periplasmic enzyme that – to exert its action – necessitates neither ATP nor other cofactors, and consistently, is independent of de novo synthesis of lipids. A heme-binding site typical of cytochrome c-type proteins is present in the predicted Cti polypeptide indicating a reaction mechanism that renounces temporary saturation of the double bond. Due to its direct correlation with toxicity, cis–trans-isomerization is a potential biomarker for recording solvent stress or changes of other environmental conditions.