Inter-annual stability of oligopeptide patterns of Planktothrix rubescens blooms and mass mortality of Daphnia in Lake Hallwilersee.

Baumann, Heike Irmgard and Jüttner, Friedrich (2008) Inter-annual stability of oligopeptide patterns of Planktothrix rubescens blooms and mass mortality of Daphnia in Lake Hallwilersee. Open Access Limnologica, 38 (3-4). pp. 350-359. DOI 10.1016/j.limno.2008.05.010.

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During mass developments of Planktothrix rubescens, the biomass of this cyanobacterium was collected over a
period of four consecutive years (2002–2005) from Lake Hallwilersee, Switzerland. To avoid any shifts in analytical
separation and sensitivity, the biomasses were extracted with 60% aqueous methanol at the end of the investigation
period and were analysed within 1 week by LC-ESMS. A new mass spectrometric method to quantify oligopeptides
was introduced. The sum of all major molecular species (quasi-molecular ion, double charged ion, adducts, dimers and
molecular ions that had lost a water molecule) rather than just the signal of the quasi-molecular ion was used to
determine the total abundance of oligopeptides. This procedure has become necessary because the variable presence of
inorganic ions and the varying conditions of the mass spectrometric source strongly affect the formation of the
different molecular species. Several anabaenopeptins, oscillapeptins and planktocyclins were found. [Asp3,
Dhb7]microcystin-RR was the major microcystin. The oligopeptide patterns were relatively stable over the
investigation period of 4 years. In June 2005, a mass mortality of Daphnia was observed. The dead Daphnia, which
floated on the surface of the lake, were collected and analysed for oligopeptides. Planktocyclin and planktocyclin
sulfoxide, which belong to the major cyclic peptides in P. rubescens, were found in the carcasses of Daphnia, but
microcystins were missing. Live zooplankton of the epilimnion was represented by both Daphnia and copepods, while
the patches of dead zooplankter on the lake surface were free of copepods and contained only Daphnia. Protease
inhibitors rather than microcystins are discussed as the major bioactive compounds for grazer defence of P. rubescens.

Document Type: Article
Keywords: Daphnia; Planktothrix rubescens; Mass mortality; Oligopeptide; Inter-annual variation; Planktocyclin; Cyanobacterial toxin; Protease inhibitor; Quantification of mass spectrometric signals
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.limno.2008.05.010
ISSN: 0075-9511
Date Deposited: 05 Jan 2009 16:30
Last Modified: 28 Sep 2017 13:18

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