Identification and differentiation of brewery isolates of Pectinatus sp. by Matrix-Assisted-Laser Desorption-Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS)

Members of the genus Pectinatus (P.) are feared contaminants in the brewing industry as their growth in beer results in the production of metabolites, which cause serious off-flavors such as hydrogen sulfide. Thus, identification and differentiation of the species P. cerevisiiphilus, P. frisingensis and P. haikarae is of vital interest. Nineteen isolates of Pectinatus were analyzed by matrix-assisted-laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Reference spectra were recorded for four isolates representing the three species P. cerevisiiphilus, P. frisingensis and P. haikarae, which enabled reliable identification of the remaining fifteen isolates as P. frisingensis. All isolates were further examined to investigate MALDI-TOF MS's potential to differentiate between various isolates of Pectinatus species. Upon generation of reference database spectra, sixteen out of nineteen isolates could be distinguished based on differences in their MALDI-TOF MS fingerprint. Two out of three misidentifications occurred between highly similar isolates originating from the same brewery. As MALDI-TOF MS spectra were reliably assigned to the corresponding isolate in more than 80 % of all cases, the application of MALDI-TOF MS could help to track contaminants in the production system and to monitor efforts to eliminate them.