Grazing by amoebae causes a dramatic shift in the genetic structure of a bloom of the cyanobacterium Microcystis

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1 Grazing by amoebae causes a dramatic shift in the genetic structure of a bloom of the cyanobacterium Microcystis Jeroen Van Wichelen 1, Pieter Vanormelingen 1, Ineke van Gremberghe 1, Ann-Eline Debeer 1, Karen Soenen 1, Tine Verstraete 1, Sofie D Hondt 1, Renaat Dasseville 1, Katleen Van der Gucht 1, Jean-Pierre Descy 2, Geoffrey Codd 3 & Wim Vyverman 1 1 Research group Protistologie & Aquatische Ecologie, Ghent University, Krijgslaan 281 S8, 9 Gent, Belgium 2 Laboratory of Freshwater Ecology, University of Namur, 5 Namur, Belgium 3 Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, United Kingdom 4 Centre d ingénierie des Protéines, Institut de Chimie B6, Université de Liège, B-4 Liège, Belgique

2 Otsuka et al. 21. Int. J. Sist. Evol. Micr. 51:

3 Sampled blooms in Flanders About 4 % of cyanobacterial blooms contained microcystins

4 Leeuwenhofvijver (Drongen)

5 Tiense broeken

6 l/m² % of nursed birds in Belgian wildlife rehabilitation centers h C Environmental factors favouring avian botulism in Belgium botulism victims amongst waterfowl 16 * average summer (May-October) temperature x Climate change Evolution in average temperature in Belgium (Ukkel, ) (source KMI) summer (May-October) sunshine precipitation in summer (May-October) ratio summer sunshine/summer precipitation source: Vogelbescherming Vlaanderen x source: KMI Same requirements for proliferation Cyanobacteria

7 Problems in lakes of high recreational value Gavers, Harelbeke 3-4/27 Schulensmeer, Lummen 8-9/27

8 Microcystis ITS rdna diversity High local and regional ITS diversity of Microcystis blooms Average number of ITS genotypes per sample: 3.6 (range: 1-1). Correlation with environmental variables? Microcystis functional diversity Consequences for bloom dynamics and food web structure

9 Park Westveld, Sint-Amandsberg % O2 ph 1, 9,5 9, 8,5 8, 7,5 7,

10 µg C L-1 Microcystis microscopic counts 25 2 solitary Microcystis cells Microcystis aeruginosa Microcystis viridis M M

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12 µg C L-1 Amoebae seem to cause a temporary bloom collapse and an abrupt change in population structure solitary Microcystis cells Microcystis aeruginosa Microcystis viridis amoebae N ml

13 % % The amoebae seem to have certain food preferences are they selective feeders? M. aeruginosa-type M. viridis-type amoebal infestation 'aeruginosa' amoebal infestation 'viridis' N colonies ml -1 N colonies ml

14 Consequences for bloom toxicity? 25 2 µg C L-1 solitary Microcystis cells Microcystis aeruginosa Microcystis viridis total MC LR µg l

15 A recurrent phenomenon? 25 2 Microcystis unicells M. aeruginosa-type Microcystis viridis-type amoebae µg C L -1 4 N ml

16 % Influence of climatological conditions? N colonies ml -1 % M. aeruginosa-type M. viridis-type amoebal infestation 'aeruginosa' amoebal infestation 'viridis' N colonies ml

17 µg C L-1 Verification of specificity of amoebae grazing: experiments 25 2 Microcystis aeruginosa Microcystis viridis amoebae N ml -1 Monocultures of different Microcystis-strains in WC-medium Amoebal cultures with mixed Microcystis-cultures as prey Cultivated at 24 C and 12/12 hour dark/light regime

18 First preliminary experiments W168. W3. W32 auruginosa aeruginosa aeruginosa 1 W2 W2 W24 viridis viridis viridis 6 strains (3 M.viridis -type, 3 M. aeruginosa -type) 2 amoebal strains differences in biomass at beginning and end of incubation period measured by absorbance of chl a

19 Amoebal strain 1 p <,1 n.s. n.s.

20 Biomass (mg C/l) 8 Day 6 n.s. p =,9 p <,1 n.s without amoebae with amoebae 2 1 W168 W2 W2 W24 W3 W32 Microcystis-strains Amoebal strain 2

21 Conclusions and perspectives Grazing by amoebae can cause a temporary bloom collapse and a sudden shift in genetic structure of a Microcystis bloom. Preliminary experiments show food preference by the observed amoebae for different M. aeruginosagenotypes while M. viridis seems less susceptible. Future work includes the characterisation of the different amoebal strains and more standardized experiments to unravel genetic variation in Microcystis resistance against grazing by amoebae to complement patterns observed in nature.

22 Biomass M. aeruginosa (mg C l -1 ) Biomass M. viridis (mg C l -1 ) Voedselpreferentie-experimenten najaar 29 Invloed van Microcystis-stam en amoeben-stam (juli 29) 4 stammen M. aeruginosa: drie 1-cellig (W168, W3, W32), één kolonievormend (M31) 4 stammen M. viridis: allen kolonievormend (W2, W15, W2, W24) 4 amoeben stammen, twee dactylopoidale type, twee reticulate type control +A1 +A2 +A16 +A control +A1 +A2 +A16 +A Sterk begrazingseffect op M. aeruginosa en niet op M. viridis

23 mg C l W-168 amoeba 16 amoeba 1 amoeba 21 amoeba 2 control mg C l W-15 amoeba 16 amoeba 1 amoeba 21 amoeba 2 control mg C l W-3 amoeba 16 amoeba 1 amoeba 21 amoeba 2 control mg C l W-2 amoeba 16 amoeba 1 amoeba 21 amoeba 2 control 2 1 mg C l W-32 amoeba 16 amoeba 1 amoeba 21 amoeba 2 control mg C l W-2 amoeba 16 amoeba 1 amoeba 21 amoeba 2 control begrazingseffect niet homogeen voor M. aeruginosa, wel voor M. viridis

24 Biomass M. aeruginosa (mg C l -1 ) Biomass M. viridis (mg C l -1 ) Invloed van Microcystis-morfologie op amoeben begrazing (september 29) M. aeruginosa-stam M31: enkelcellig, kolonies, mengsel M. viridis-stam W24: enkelcellig, kolonies, mengsel Amoebenstam: A Colonies-A21 Colonies-Control Mixture-A21 Mixture-Control Single cells-a21 Single cells-control Colonies-A21 Colonies-Control Mixture-A21 Mixture-Control Single cells-a21 Single cells-control Morfologie speelt geen rol bij beide morphotypes

25 Graassnelheid van amoeben op M. aeruginosa (september 28) M. aeruginosa-stam M31: mengsel (15 mg C L-1) Amoebenstam: A21 (1. ind. ml-1) 12 dagen incubatie in donker 2 M31c-C M31c-A Er vindt begrazing plaats, maar traag