Determination of oligopeptide diversity within a natural population of Microcystis spp. (cyanobacteria) by typing single colonies by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Abstract

Besides the most prominent peptide toxin, microcystin, the cyanobacteria Microcystis spp. have been shown to produce a large variety of other bioactive oligopeptides. We investigated for the first time the oligopeptide diversity within a natural Microcystis population by analyzing single colonies directly with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The results demonstrate a high diversity of known cyanobacterial peptides such as microcystins, anabaenopeptins, microginins, aeruginosins, and cyanopeptolins, but also many unknown substances in the Microcystis colonies. Oligopeptide patterns were mostly related to specific Microcystis taxa. Microcystis aeruginosa (Kütz.) Kütz. colonies contained mainly microcystins, occasionally accompanied by aeruginosins. In contrast, microcystins were not detected in Microcystis ichthyoblabe Kütz.; instead, colonies of this species contained anabaenopeptins and/or microginins or unknown peptides. Within a third group, Microcystis wesenbergii (Kom.) Kom. in Kondr., chiefly a cyanopeptolin and an unknown peptide were found. Similar patterns, however, were also found in colonies which could not be identified to species level. The significance of oligopeptides as a chemotaxonomic tool within the genus Microcystis is discussed. It could be demonstrated that the typing of single colonies by MALDI-TOF MS may be a valuable tool for ecological studies of the genus Microcystis as well as in early warning of toxic cyanobacterial blooms.

FIG. 1

Positive-ion MALDI-TOF mass spectra (m/z range 550 to 1,100 Da) of Microcystis strains PCC 7806 (axenic) (A), PCC 7813 (axenic) (B), HUB 5-3 (unialgal) (C), HUB 5-2-4 (unialgal) (D), and HUB 063 (unialgal) (E). For structure assignments, see Table 2.

FIG. 2

Positive-ion MALDI-TOF mass spectra (m/z range, 600 to 1,100 Da) of the entire Microcystis population (A) and of colonies of M. aeruginosa (B), M. ichthyoblabe (C), and Microcystis sp. (D) in Lake Wannsee on 24 August 1999. For structure assignments, see Table 2.

FIG. 3

PSD spectrum of microcystin-LR: m/z 995 [M + H]⁺, 861 [M − 134 (Adda side chain) + H]⁺, 599 [Arg−Adda−Glu + H]⁺, 375 [C₁₁H₁₄O−Glu−Mdha]⁺, 286 [Arg−MeAsp + H]⁺, 213 [Glu−Mdha + H]⁺, 155 [Mdha−Ala + H]⁺, 135 [PhCH₂CH(OCH₃)]⁺, and 70 [Leu − CO + H]⁺.

FIG. 4

Molecular masses (m/z) oligopeptides and unknown components in the range of m/z 500 to 1,100 Da detected in colonies of M. aeruginosa, M. ichthyoblabe, and M. wesenbergii. Symbols for substance classes: open diamonds, aeruginosin; open circles, microginin; open triangles, anabaenopeptin; open squares, microcystin; solid diamonds, cyanopeptolin; small solid rectangles, unknown components. For structure assignments of compounds, see Table 2.

FIG. 5

Molecular masses (m/z) of oligopeptides and unknown components in the range of m/z 500 to 1,100 Da detected in colonies of Microcystis spp. Symbols for substance classes: open diamonds, aeruginosin; open circles, microginin; open triangles, anabaenopeptin; open squares, microcystin; solid diamonds, cyanopeptolin; small solid rectangles, unknown components. For structure assignments of compounds, see Table 2.