Electroporation and mass spectrometry: a new paradigm for in situ analysis of intact proteins direct from living yeast colonies

Yeasts constitute an oft-neglected class of pathogens among which the resistance to first-line treatments, attributed in part to mutations in efflux pumps, is rapidly emerging. Their thick, chitin-reinforced cell walls render cell lysis difficult, complicating their analysis and identification by methods routinely used for bacteria, including matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Liquid extraction surface analysis mass spectrometry (LESA-MS) has previously been applied to the analysis of intact proteins from Gram-positive and Gram-negative bacterial colonies sampled directly on solid nutrient media. To date, a similar analysis of yeast colonies has not proved possible. Here we demonstrate the rapid release of intact yeast proteins for LESA-MS by electroporation using a home-built high-voltage device designed to lyse cells grown in colonies on agar media. Detection and identification of previously inaccessible proteins from baker’s yeast Saccharomyces cerevisiae, as well as two clinically relevant yeast species (Candida glabrata and Cryptococcus neoformans), is shown. The electroporation approach also has the potential to be translated to other mass spectrometric analysis techniques, including MALDI and various ambient ionization methods.