AimsTo establish the role of cardiolipin (CL) of the membrane in response to the presence of tetradecyltrimethylammonium in Pseudomonas putida A (ATCC 12633). Methods and ResultsTwo ORFs of Ps.putida A (ATCC 12633), which in Ps.putida KT2440 encode the putative CL synthase genes cls and cls2, were cloned, sequenced and mutated. Only the double mutant lacking cls and cls2 showed a reduction of the CL content, 83% lower than the amount produced by the wild-type. Accompanying this change was a 40% decrease in the content of unsaturated fatty acid. Consequently, the membrane of the mutant was more rigid than the one of the parental strain, as observed using fluorescence polarization techniques. The mutant strain showed reduced viability in the presence of tetradecyltrimethylammonium. The incorporation of exogenous CL into its membrane relieved sensitivity to the cationic detergent. ConclusionsPseudomonas Putida cells with low levels of CL die in the presence of tetradecyltrimethylammonium, because they cannot counter the fluidizing effect of the cationic surfactant. Significance and Impact of the StudyThe modification in the membrane phospholipids composition allows knowing the adaptation strategy of Ps.putida when these bacteria are exposed to cationic surfactant.