Application of MALDI Biotyper to cyanobacterial profiling

Rationale Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) has been used for bacterial profiling. A few reports have shown MALDI‐MS profiling of isolated/cultured cyanobacteria; however, these applications have been limited. In this study, we have investigated whether rapid profiling and differentiation of cyanobacteria including harmful genera Microcystis and Anabaena (Dolichospermum) can be performed by MALDI Biotyper analysis of intact cells. Methods Twenty‐two cyanobacterial strains including 12 Microcystis, 7 Anabaena, 1 Pseudanabaena, 1 Planktothrix, and 1 Synechocystis were cultured. Also, natural pond water containing cyanobacteria was collected. Intact cyanobacterial cells were deposited on a target plate, and analyzed using an Autoflex Speed MALDI‐TOF mass spectrometer with Biotyper software. Mass spectra obtained from m/z 2000 to 20000 were used for clustering and spectral library searching of cyanobacterial strains. Results MALDI‐MS analysis of cultured cyanobacterial cells showed clear ion signals under optimized conditions. Hierarchical clustering of mass spectra using Biotyper resulted in a tight cluster of Microcystis strains which was clearly differentiated from a cluster of Anabaena strains. Spectral library searching was able to identify Microcystis aeruginosa NIES‐298 and Synechocystis sp. PCC 6803 even when these two cells were mixed. Furthermore, cyanobacterial cells in the pond water were successfully classified as Anabaena. Conclusions We have demonstrated that MALDI‐MS in combination with Biotyper analysis is applicable to cyanobacterial profiling. Increasing the size of the spectral library may facilitate monitoring of cyanobacteria in crude cyanobacterial blooms. Copyright © 2016 John Wiley & Sons, Ltd.