Comprehensive Analysis of Microbial Lipids in Environmental Samples Through HPLC-MS Protocols

Abstract

Diversification and fine-tuning of membrane lipids has been a crucial step in allowing taxonomic diversification of microbial life, ecological expansion into new or changing habitats, and exploration of novel resources. This results in a strong association between lipid composition and taxonomy, environmen- tal conditions, and some particular metabolic activities, an association that is the base of the lipid biomarker concept. Applied to environmental and geological samples, lipid biomarkers are able to provide a wealth of information: recalcitrant apolar lipids and relatively labile intact polar lipids can be informative on geological and biological timescales, respectively.We here provide an overview of the current state of lipid biomarker analysis by high-performance liquid chromatography mass spectrometry (HPLC-MS), with an emphasis on applications to complex environmental samples. Coupled to mass spectrometry through electrospray ionization, normal-phase or hydrophilic interaction liquid chromatography provides straightforward anal- ysis of intact polar lipids (IPLs) according to their headgroups. Implementation of reversed-phase separa- tion, on the other hand, offers to dramatically expand the analytical window of LC-MS amenable lipids and besides IPLs may, for example, target apolar glycerolipids, quinones, pigments, and bacteriohopanepolyols. An outlook to the potential of ultrahigh-resolution mass spectrometry to revolutionize several aspects of lipid biomarker analysis in the near future is also provided.