Grouping Myxococci (Corallococcus) Strains by Matrix-Assisted Laser Desorption Ionization Time-of-Flight (MALDI TOF) Mass Spectrometry: Comparison with Gene Sequence Phylogenies

Nine Corallococcus isolates and three type strains of Corallococcus species were characterized by Intact Cell Mass Spectrometry using Matrix Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) mass spectrometry. The resulting phenetic clustering was compared to the phylogenetic grouping based upon sequences of two housekeeping genes. The three dendrograms of relatedness resembled each other in that the isolates were highly similar to the type strains of Corallococcus exiguus and Corallococcus coralloides, while Corallococcus macrosporus and Myxococcus xanthus were more distantly related. While certain pairs of organisms were recovered by spectrometry and genes sequence analysis, others were detected by two of the three approaches. The degree of similarity determined by sequence analysis of the two genes was not higher than that revealed by MALDI-TOF analysis. The results show that the spectral profile, consisting of about 25 to 45 masses ranging between 2 and 20 kDa, have indeed taxonomic significance, confirming literature data that ribosomal proteins and certain housekeeping proteins are responsible for the masses obtained. Provided the availability of a database of type strains, MALDI-TOF analysis of unknown strains appears to be a rapid and inexpensive method to taxonomically cluster environmental isolates, expanding the spectrum to strains other than those of medical importance predominantly investigated so far.