Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometric analysis of extrapolysaccharides of Escherichia coli.

RATIONALE

Conventional studies of extracellular polymeric substances (EPS) typically require elaborate separation procedures or complicated sample pretreatment processes such as purification by dialysis and lyophilization. The objective of this study is to demonstrate the use of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) as powerful techniques for direct analysis of EPS secreted by E. coli.

METHODS

We have compared the extraction efficiency of two widely used extraction methods including physical extraction (room-temperature centrifugation and high-speed centrifugation) and chemical extraction using EDTA and formaldehyde. We specify the most favorable extraction method and the analyte to extractant concentration with respect to mass spectrometric analysis of EPS, based on the results obtained from ESI-MS and MALDI-MS analysis.

RESULTS

Chemical extraction methods were found to be more efficient than physical extraction methods. Of the chemical extractants, EDTA was found more effective compared to formaldehyde and gave more EPS peaks during ESI- and MALDI-MS analysis. We report the classification of E. coli EPS into loosely bound, bound and tightly bound EPS based on a simple modification of an existing methodology. Our studies showed that ESI-MS was very effective for <300 Da EPS studies and MALDI-MS more suitable for rapid analysis of EPS above mass range 400 Da.

CONCLUSIONS

This is a preliminary study reporting for the first time the feasibility of ESI-MS and MALDI-MS techniques for the analysis of bacterial EPS without prior complicated purification and separation methodologies.