Abstract
Top-down identification of proteins by liquid extraction surface analysis (LESA) mass spectrometry has previously been reported for tissue sections and dried blood spot samples. Here, we present a modified "contact" LESA method for top-down analysis of proteins directly from living bacterial colonies grown in Petri dishes, without any sample pretreatment. It was possible to identify a number of proteins by use of collision-induced dissociation tandem mass spectrometry followed by searches of the data against an E. coli protein database. The proteins identified suggest that the method may provide insight into the bacterial response to environmental conditions. Moreover, the results show that the "contact" LESA approach results in a smaller sampling area than typical LESA, which may have implications for spatial profiling.
Highlights
The development of ambient mass spectrometry techniques such as desorption electrospray ionization (DESI)[13] and liquid extraction surface analysis (LESA)[14] have enabled direct sampling of bacterial colonies with little or no sample preparation
A wide variety of small molecules has been detected from bacterial colonies by techniques such as DESI, nano-DESI, LESA, and the continuous flow-probe coupled to mass spectrometry, analysis of intact proteins from bacteria by ambient mass spectrometry has not previously been reported
When setting up a LESA method, there are several parameters which are user-defined and can affect the extraction efficiency including the solvent system used for extraction and the height to which the pipet descends above the sample surface
Summary
The development of ambient mass spectrometry techniques such as desorption electrospray ionization (DESI)[13] and liquid extraction surface analysis (LESA)[14] have enabled direct sampling of bacterial colonies with little or no sample preparation. They identified 73 proteins in the mass range of 4−36 kDa. The development of ambient mass spectrometry techniques such as desorption electrospray ionization (DESI)[13] and liquid extraction surface analysis (LESA)[14] have enabled direct sampling of bacterial colonies with little or no sample preparation.
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