Lipidomics of homeoviscous adaptation to low temperatures in Staphylococcus aureus utilizing exogenous straight-chain unsaturated fatty acids over biosynthesized endogenous branched-chain fatty acids

Abstract

It is well established that Staphylococcus aureus can incorporate exogenous straight-chain unsaturated fatty acids (SCUFAs) into membrane phospho- and glyco-lipids from various sources in supplemented culture media, and when growing in vivo in an infection. Given the enhancement of membrane fluidity when oleic acid (C18:1{Delta}9) is incorporated into lipids, we were prompted to examine the effect of medium supplementation with C18:1{Delta}9 on growth at low temperatures. C18:1{Delta}9 supported the growth of a cold-sensitive, branched-chain fatty acid (BCFA)-deficient mutant at 12{degrees}C. Interestingly, we found similar results in the BCFA-sufficient parental strain. We show that incorporation of C18:1{Delta}9 and its elongation product C20:1{Delta}9 into membrane lipids was required for growth stimulation and relied on a functional FakAB incorporation system. Lipidomics analysis of the phosphatidylglycerol (PG) and diglycosyldiacylglycerol (DGDG) lipid classes revealed major impacts of C18:1{Delta}9 and temperature on lipid species. Growth at 12{degrees}C in the presence of C18:1{Delta}9 also led to increased production of the carotenoid pigment staphyloxanthin; however, this was not an obligatory requirement for cold adaptation. Enhancement of growth by C18:1{Delta}9 is an example of homeoviscous adaptation to low temperatures utilizing an exogenous fatty acid. This may be significant in the growth of S. aureus at low temperatures in foods that commonly contain C18:1{Delta}9 and other SCUFAs in various forms. IMPORTANCEWe show that S. aureus can use its known ability to incorporate exogenous fatty acids to enhance its growth at low temperatures. Individual species of phosphatidylglycerols and diglycosyldiacylglycerol bearing one or two degrees of unsaturation derived from incorporation of C18:1{Delta}9 at 12{degrees}C are described for the first time. In addition, enhanced production of the carotenoid staphyloxanthin occurs at low temperatures. The studies describe a biochemical reality underlying in membrane biophysics. This is an example of homeoviscous adaptation to low temperatures utilizing exogenous fatty acids over the regulation of the biosynthesis of endogenous fatty acids. The studies have likely relevance to food safety in that unsaturated fatty acids may enhance growth of S. aureus in the food environment.