Whole-cell matrix-assisted laser desorption/ionization mass spectrometry for rapid identification of...

The potential of whole-cell matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) for the discovery of microorganisms that produce lantibiotics and/or bacteriocins in the mass range 3-5 kDa is demonstrated. Cells of the antibiotic-producing model strain Bacillus subtilis ATCC 6633 were grown on Landy agar plates, and prepared with a 9:1 mixture of 2,5-dihydroxybenzoic acid and 2-hydroxy-5-methoxybenzoic acid (DHBs) as matrix using the bottom-layer method. Time-course analyses showed that cells grown for 1-2 days on agar plates gave the best results in terms of intensity of the bacteriocin/lantibiotic signals. Even after storage of matrix-crystal-embedded cells for several days high-resolution spectra (>10,000) could be obtained. To verify the applicability of this technique, different Bacillus wild-type and gene deletion mutant cells were analyzed. In most of the cases the known antibiotic phenotype of the producer could be corroborated by whole-cell MALDI-TOFMS, particularly for the lantibiotics subtilin and ericin. The preparation recipe for whole-cell analysis by MALDI-TOF was also highly sensitive for hydrophobic lipopeptide antibiotics like surfactin, mycosubtilin, fengycin, and bacillomycin in the lower mass range (1-1.5 kDa).