Phospholipid-derived fatty acids

Phospholipid-derived fatty acids (PLFA) are widely used in microbial ecology as chemotaxonomic markers of bacteria and other organisms. Phospholipids are the primary lipids composing cellular membranes. Phospholipids can be saponified, which releases the fatty acids contained in their diglyceride tail. Once the phospholipids of an unknown sample are saponified, the composition of the resulting PLFA can be compared to the PLFA of known organisms to determine the identity of the sample organism. PLFA analysis may be combined with other techniques, such as stable isotope probing to determine which microbes are metabolically active in a sample. PLFA analysis was pioneered by D.C. White, MD, PhD, at the University of Tennessee, in the early to mid 1980s.

Phospholipid fatty acids (PLFA) are an essential structural component of all microbial cellular membranes. PLFA analysis is a technique widely used for estimation of the total biomass and to observe broad changes in the community composition of the living microbiota of soil and aqueous environments. There has been a surge of interest in PLFAs in recent years, evident from the large increase in peer-reviewed journal references on the subject. However, there is increasing concern that some researchers are assigning PLFAs to specific microbial classes when in fact those PLFAs are present in a broad range of life forms. Phospholipids can occur in many biological classes (such as in plant roots, fungi, as well as in soil bacteria), so care has to be taken in over-assigning PLFA biomarkers to the wrong class. Even though phospholipids occur in many different life forms, the fatty acid side chains between differing life forms can be quite unique. Polyunsaturated fatty acids (e.g. 18:3 ω3c) are found in plants, algae and cyanobacteria, but are often not present in bacteria. Monounsaturated fatty acids (particularly at the omega-7 position), odd-chain saturated fatty acids (e.g. 15:0), branched-chain fatty acids (mainly iso/anetiso and 10-methyl) and cyclopropane fatty acids (e.g. 19:0 cyclo ω7c) are mostly synthesized by bacteria. The monounsaturated fatty acid, 16:1 ω5c, is mostly synthesized by Arbuscular mycorrhizal fungi (AMF) and the polyunsaturated fatty acid, 18:2 ω6c (Linoleic acid), is mostly synthesized by Ectomycorrhizal fungi.

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