Phospholipid Fatty Acid (PLFA) Analysis: A Robust Indicator for Soil Health?

Phospholipid fatty acid, commonly referred to as PLFA, is an analytical concept that emerged in the late 1980’s for estimating composition of soil microbial communities [1]. While it is popular to describe the test as determining types of microbes in soils, in fact PLFA reveals the content of differing extractable phosphorylated-lipids recognized to be cell-wall constituents of microbes [2] extractable from soil with organic solvents. The advantage of PLFA is frequently characterized by contrasting it to the recognized difficulties that traditional microbiological cultural methods encounter in successful isolation and culturing of species present. PLFA is an indirect and multi-step process. After successful delineation of the range of lipids observed the analyst normally proceeds further to decide on assignments of groups of specific lipids as biomarkers or “signatures” for classes or genera of organisms. This selection process is not necessarily straight-forward and is based on accumulated evidence corroborating structural aspects of the relationships. The assignments generally include terminally branched saturated fatty acids to gram-positive bacteria, monounsaturated fatty acids to gram-negative bacteria, mid-branched saturated fatty acids for actinomycetes, and polyunsaturated fatty acids to fungi.