Table 1.
Identification of marine bacteria from artificial ballast water.*.
Figure 1.
MALDI-TOF mass spectrograms, (panel A) and 16S rRNA gene sequence phylogram, (panel B) for four Vibrio isolates from the North Sea.
Panel A, the X axis indicates the mass to charge ratios (m/z) of each peak and the Y axis for each individual plot indicates intensity of the peaks. The identification result using Biotyper software is shown at the top-right corner of each plot followed by the type strain designation. Several mass spectral peaks are common between the isolates and a few show differences, examples of similar peaks are aligned by dotted lines. Panel B, distance phylogram tree of the isolates, over 1500 nucleotides.
Table 2.
Mass spectral peak list comparing three marine bacterial species isolated in this study with previously published data.*.
Figure 2.
MALDI-TOF spectra of two isolates of Vibrio, S17 and S42.
Although Biotyper software identified these isolates as strains of V. alginolyticus, they were identified as V. rotiferianus and V. natriegens respectively by 16S rRNA gene BLAST search. Panel A shows the spectra for the range m/z 2,000–20,000 and panel B is an enhanced view of the m/z 4,000–7,500 range. The X axis indicates the mass-to-charge ratios (m/z) and the Y axis in each individual plot indicates relative intensities of the ions. Examples of peaks that are not common between the two isolates are indicated by arrows.
Figure 3.
MALDI-TOF mass spectra of two Serratia species.
16S rRNA sequencing indicated that isolates S21 and S33 were both Serratia plymuthica. However there are differences in their mass-spectral patterns. The whole m/z 2,000–20,000 spectra of the two isolates are shown in the main panel (left). The small panels show highlighted regions of the spectra with more significant the mass-to-charge ratio (m/z) differences.
Figure 4.
MALDI-TOF mass spectra for Enterococcus isolates.
16S rRNA gene analysis indicated that isolates S15 and S44 are the same species (E. hirae). However the protein fingerprints were not quite the same. The identification result using Biotyper software is shown at the top-right corner followed by the strain designations.
Figure 5.
MALDI-TOF mass spectra of five Pseudomonas isolates.
Species of Pseudomonas are distinguishable by their protein fingerprints. Examples of the peaks that are common between species are shown by dotted lines; peaks that can be used for differentiation of the isolates are indicated by arrows.
Figure 6.
MALDI-TOF mass spectra from Pseudoalteromonas (PAL) isolates.
The mass spectrum of P. tetraodonis was added to the database after identification of an isolate by 16S rRNA gene sequencing. Isolate S49, with some similarities to the mass spectral pattern of PAL is also included in the comparisons. Panel A shows spectra of all PAL isolates for the range of m/z 3000–10000. Panels B to E show similarities and differences between the PAL isolates at different m/z. The order of isolates in all panels is as labelled in panel A.
Figure 7.
Heat-map of Pseudoalteromonas (A) and Pseudomonas (B) isolates generated by the Biotyper software.
The spectra were split into 8 or 11 groups according to the directory structure. Red colours indicate closely related groups with identical peaks, and blue colours mark non-related groups.
Figure 8.
Comparison of Pseudomonas stutzeri and Proteus vulgaris MALDI-TOF mass spectra.
Isolates S04, S24 and S38 were identified as P. stutzeri through 16S rRNA gene sequencing; however isolate S24 showed a different peak pattern and was identified as Proteus vulgaris by the Biotyper software. Examples of common peaks are indicated by vertical lines and unique peaks are indicated by the arrows.
Table 3.
CCV analysis of MALDI-TOF data of four Vibrio isolates using the in-house method developed for this study.*.
Figure 9.
Examples of in-house CCV analysis of Vibrio isolates S14 and S27 (A) and S14 and S32 (B).
Panel C shows the spectrograms of Vibrio isolates S14, S27, S30, and S32.
Table 4.
In-house CCV analysis of MTB fingerprints of Pseudoalteromonas isolates from the North Sea.
Table 5.
In-house CCV analysis of MTB fingerprints of Pseudomonas isolates from the North Sea.