Strategies and data analysis techniques for lipid and phospholipid chemistry elucidation by intact cell MALDI-FTMS

Abstract

Ions attributed to lipids and phospholipids are directly observed by desorption from whole bacteria using intact cell (IC) matrix-assisted laser desorption-ionization (MALDI) Fourier transform mass spectrometry (FTMS). Saccharomyces cerevisiae are grown in rich media broth, concentrated, and applied directly to the MALDI surface without lysis or chemical treatment. FTMS of MALDI ions gives excellent signal to noise ratios with typical resolving powers of 90,000 and mass precision better than 0.002 Da. Use of accurate mass measurements and a simple set of rules allow assignment of major peaks into one of twelve expected lipid classes. Subsequently, fractional mass versus whole number mass plots are employed to enhance visual interpretation of the high-resolution data and to facilitate detection of related ions such as those representing homologous series or different degrees of unsaturation. This approach, coupled with rules based on bacterial biochemistry, is used to classify ions with m/z up to about 1000. Major spectral peaks in the range m/z 200-1000 are assigned as lipids and phospholipids. In this study, it is assumed that biologically-derived ions with m/z values lower than 1000 are lipids. This is not unreasonable in view of the facts that molecular weights of lipids are almost always less than 1000 Da, that the copy numbers for lipids in a cell are higher than those for any single protein or other component, and that lipids are generally collections of distinct homologous partners, unlike proteins or other cell components. This paper presents a new rapid lipid-profiling method based on IC MALDI-FTMS.

Lipid fingerprinting of Bacillus spp. using online MALDI-TOF mass spectrometry

“…33 MALDI-TOF MS has also been applied to obtain abundant, accurate mass ion signals of the phospholipids in bacteria. [34][35][36][37][38][39] Therefore, the characterization of lipids in bacteria and other microorganisms plays a crucial role for taxonomic identification, differentiation of pathogenic species, and understanding of metabolic processes under normal or stressed growth conditions. However, there are few reports on the application of online MALDI-TOF MS coupling with lipid profiling for identification of bacterial species.…”

High Accuracy Mass Measurement Approach in the Identification of Phospholipids in Lipid Extracts: 7 T Fourier-transform Mass Spectrometry and MS/MS Validation

“…4,[10][11][12][13][14][15][16][17] Even with the disadvantage of relatively low sensitivity, the direct-infusion ESI-FTMS approach is very easy to implement and also provides a good method to compare the global lipid distributions of two total lipid extracts under inspection.…”

“…[1][2][3] FTMS can provide a mass resolution on the order of 90,000 below m/z 1,000 and allow a mass accuracy of 10 ppm or better in a broad band analysis. 4 These advantages become even more powerful in the analysis of small molecular species such as lipids that generally have relatively low mass values and exist within a narrow mass range, particularly, m/z 400-1,000. [5][6][7][8] Indeed, a number of groups have shown that FTMS is a very effective tool in lipid analysis.…”

“…[15][16][17] Wilkins and coworkers developed a data analysis strategy that utilizes a mass defect plot (fractional mass versus whole number mass) for the identification of lipid species detected in the high-resolution MALDI FTMS spectra. 4,16,17 Using only accurate mass measurements and a simple set of rules related to mass defects, a majority of ion-peaks below m/z 1,000 could be distinguished into twelve lipid classes. The classified lipids were further identified using their in-house lipid database with more than 50,000 entries.…”

Rapid lipid profiling of bacteria by online MALDI-TOF mass spectrometry

“…MALDI have been applied to analyze lipid extracts or lipids in whole cell bacteria [14][15][16][17].…”