Characterization of 1-acyl-sn-glycerol-3-phosphate acyltransferase from a polyunsaturated fatty acid-producing bacterium, Shewanella livingstonensis Ac10

Abstract

Bacterial membranes consist of proteins and a phospholipid bilayer, and most membrane phospholipids are glycerolipids containing 2 fatty acyl chains. These phospholipid acyl chains play an important role in survival functions, such as adaptation to temperature , osmotic pressure, solvent and salinity changes in vivo or in the passive permeability of hydrophobic molecules, active solute transport, and lipid protein interaction. The adjustment in the fatty acid composition that maintains the biophysical properties of membranes is interpreted as an adaptation mechanism, which modifi es the permeability and fl uidity of the phospholipid bilayer to minimize energy expenditure, thus resulting in optimization of their growth. In addition to these biophysical properties of the membrane, some phospholipids containing specific acyl chain, such as the platelet activation factor and lung surfactant, can contribute to peculiar bioactivity in eukaryotes. However, in prokaryotes, such bioactive lipids have been scarcely reported except that the phosphatidylethanolamine (PE) containing specifi c acyl chains can act as an extracellular signaling molecule in Myxococcus xanthus 6) and Pseudomonas aeruginosa. Eicosapentaenoic acid (EPA; 20:5) is an omega-3 polyunsaturated fatty acid, which is regarded as a vital nutrient for human health. Omega-3 polyunsaturated fatty acids, EPA and docosahexaenoic acid (22:6), have been shown to play benefi cial roles in infant development, cancer, cardiovascular diseases, and mental illnesses. Shewanella livingstonensis Ac10 has been used as a model organism for the investigation of microbial cold-adaptation mechanisms. S. livingstonensis Ac10 is a psychrotrophic bacterium isolated from Antarctic seawater, which produces the EPA as a fatty acyl chain of phospholipids at low temperatures. Previous studies have shown that the EPA-less mutant of this strain exhibits cold-sensitive phenotypes, which include growth retardation, defect in cell Original Article