Cyanobacterial Classification with the Toxicity Using MALDI Biotyper

An
abnormal growth of cyanobacteria in eutrophicated freshwaters
can cause various environmental problems. In particular, Microcystis producing hepatotoxic cyclic heptapeptides
microcystins (MCs) has been globally observed. Recent studies have
demonstrated that matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry (MALDI-TOF MS) offers a rapid classification of
cyanobacteria; however, they have not fully considered the toxicity
yet. In this study, we have performed MALDI-TOF MS for intact cyanobacterial
cells using Biotyper software and optimized their conditions to achieve
cyanobacterial classification with the toxicity. The detection mass
range used for Biotyper was extended to cover small molecules, but
their intense ions were suppressed as a function of the used instrument
Autoflex Speed, which enabled simultaneous observations of large molecular
fingerprints and small MCs with comparable ion intensity. Hierarchical
clustering of mass spectra obtained under the optimized conditions
differentiated toxic and non-toxic clusters of Microcystis strains and furthermore formed a tight cluster of non-toxic strains
possessing the MC biosynthesis gene mcyG. Spectral
libraries were expanded to >30 genera (>80 strains) under the
default
and optimized conditions to improve the confidence of cyanobacterial
classification. Consequently, spectral library searching allowed for
characterization of cyanobacteria from a field sample as mixed toxic
and non-toxic Microcystis cells, without
isolating those cells.