Pseudomonas putida 9-fatty acid desaturase: Gene cloning, expression, and function in the cationic surfactants stress

Pseudomonas putida counteract the fluidizing effect of cationic surfactants decreasing the content of membrane unsaturated fatty acid (UFA). A 9-fatty acid desaturase gene (desA) from P. putida was isolated, cloned, and successfully expressed in Escherichia coli, a 9 desaturase deficient organism. desA consists of 1185bp and codes for 394 amino acids. The deduced amino acid sequence reveals three histidine clusters and a hydropathy profile, typical of membrane-bound desaturases. Validating desA expression in E. coli cells, the amount of palmitoleic acid increased from 2.05 to 7.36%, with the concomitant increase in membrane fluidity (fluorescence polarization value decrease from 0.13 +/- 0.03 to 0.09 +/- 0.02). Also, when DesA activity was assayed in vivo, the percentage of UFA obtained from exogenous palmitic acid [1-C-14] increased 10-fold. In contrast, when cells expressing desA were exposed 15min at sublethal concentration of cationic surfactants, the amount of UFA was 82% lower than that detected in cells non-exposed. Thus, the decrease in UFA content to counteract the fluidizing effect of cationic surfactants can be correlated with reduction of DesA activity.