Mass Spectrometric Analysis of Phospholipids and Fatty Acids in Giardia lamblia

In addition to plasma membrane, Giardia lamblia contains numerous membrane-enveloped, primitive organelles, which house a variety of metabolic processes. It has been proposed earlier that this intestinal pathogen lacks the ability to synthesize the majority of its own lipids de novo and depends on supplies from outside sources. Therefore, the questions as to how this ancient eukaryote utilizes exogenous lipids and synthesizes membranes and organelles are extremely important. Does this parasite depend predominantly on remodeling pathways, in which exogenous phospholipids undergo fatty acid and headgroup replacement reactions to generate new phospholipids? To answer this, and to better understand the overall pathway, we carried out a complete lipidomic analysis using electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). The results suggest that Giardia has the ability to generate new phospholipids de novo, most likely via the remodeling pathways. Among the newly synthesized lipids, phosphatidylglycerol (PG) is the major phospholipid followed by phosphatidylethanolamine (PE). Gas chromatography-mass spectrometry (GC-MS) ana lyses indicated that Giardia also has the ability to remodel fatty acids by chain elongation and desaturation reactions. Thus, mass spectrometric analyses provided valuable information about lipid biosynthesis by Giardia and opened the possibility of investigating in greater detail the uptake and utilization of exogenous lipids for the synthesis of membranes and organelles.