Dependence of cyanobacteria defense mode on grazer pressure

Abstract

In a series of experiments we investigated the ability of a cyanobacterium of the genus Phormidium to defend itself against the ciliate grazer Furgasonia blochmanni. The experiments showed that the cyanobacterium can employ different modes of defense, depending on grazer density. Under high grazer pressure, each mat of Phormidium instantly formed a dense clump surrounded by a mucilage layer. Trichomes remaining inside such clumps were completely inaccessible to ciliates. Under medium pressure, the defense reaction was slower and consisted in enhanced sheath production by individual trichomes. The effectiveness of such a defense was also very high, as clearly reflected in the condition of the ciliates. When the pressure was low, the cyanobacteria did not exhibit any form of defense, dispersing evenly all over the bottom in a pattern similar to that observed in control mats. We conclude that the cyanobacterium is able to modify its defense reaction according to the real grazing risk.KEY WORDS: Cyanobacteria · Anti-herbivore defense · Ciliate pressure Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 27: [149][150][151][152][153][154][155][156][157] 2002 and Ph2, revealed an inducible defense capability against ciliates by means of withdrawing inside the sheaths when disturbed by grazers. Trichomes ending in empty sheaths turned out to be completely inaccessible for the ciliates (Fia8kowska & Pajdak-Stós 1997). In Phormidium autumnale, the same purpose is served by a protective layer of extracellular polysaccharides (EPS) shielding the initial piece of mat in which filaments are embedded; the defense reaction is engaged in the presence of different grazer species (Pajdak-Stós et al. 2001). However, the phenomenon was investigated only at invariable grazer density. During closer observations of the cyanobacteria mats used for feeding our ciliate cultures, we noticed interesting changes in their appearance. We suspected that those changes might be related to different ciliate densities in the culture dishes and designed a set of experiments to determine whether the cyanobacteria mode of defense depends on grazer pressure. MATERIALS AND METHODSA strain of an unidentified species of the cyanobacterium Phormidium called Ph2 in our previous paper (Fia8kowska & Pajdak-Stós 1997) and a clone of a nassulinid ciliate Furgassonia blochmanni were used for experiments. This free-living, freshwater ciliate occurs naturally in ponds and puddles along with filamentous cyanobacteria like Ph2, which form mats on the sediment surface. F. blochmanni is equipped with a cytopharyngeal apparatus, a highly specialized structure that enables the ciliate to ingest long threads of cyanobacteria (Eisler & Bardele 1986, Vigues et al. 1999.Clonal populations of experimental organisms were obtained from a single filament (Phormidium sp.) and a single cell (Furgassonia blochmanni) taken from an aquarium maintained non-axenically at the Department of Hydrobiology, Jagiellonian University, ...

Dynamics of cyanobacteria–ciliate grazer activity in bitrophic and tritrophic microcosms

“…Although the induced defence is energetically more costly than the constitutive form, it is very effective, especially when prey can adjust the extent of their reaction to the real predatory threat (Tollrian & Harvell 1999). This has been thoroughly studied in several ciliates from the genera Euplotes, Colpidium and Coleps (Kuhlmann & Heckmann 1985, Fyda & Wią ckowski 1998, Wickham & Gugenberger 2008 as well as in green algae (Lürling & Van Donk 1996) and cyanobacteria (Fia8kowska & Pajdak-Stós 2002). Our observations strongly support the results obtained by Fia8kowska & Pajdak-Stós (2002), in that Phormidium adapts its induced defence to grazer pressure and density.…”

“…This has been thoroughly studied in several ciliates from the genera Euplotes, Colpidium and Coleps (Kuhlmann & Heckmann 1985, Fyda & Wią ckowski 1998, Wickham & Gugenberger 2008 as well as in green algae (Lürling & Van Donk 1996) and cyanobacteria (Fia8kowska & Pajdak-Stós 2002). Our observations strongly support the results obtained by Fia8kowska & Pajdak-Stós (2002), in that Phormidium adapts its induced defence to grazer pressure and density. During the first 3 d of the experiment, strong pressure from Pseudomicrothorax induced a strong defence reaction in Phormidium filaments.…”

“…This could be explained as a control of active ciliate density by encystment. As a consequence of decreased density of active ciliates and thus grazer Fia8kowska & Pajdak-Stós 2002, Fyda et al 2009). The fact that empty cysts were noticeable in all treatments with Pseudomicrothorax, starting on the second day, indicates that excystment takes place regardless of predator presence (Fig.…”

Health hazards for terrestrial vertebrates from toxic cyanobacteria in surface water ecosystems

“…With regard to top-down control, cyanobacteria are usually organized in filaments and/or colonies, and may produce mucilage layers, that make it much more difficult for zooplankton to feed (graze) on cyanobacteria than on single cell structures (e.g. [38]). These authors have recently shown that the mode of defense adopted by cyanobacteria also depends on grazer pressure; i.e.…”

Use of molecular markers as indicators for winter zooplankton grazing on toxic benthic cyanobacteria colonies in an urban Colorado lake

“…Microcystis are usually organized in colonies, and may produce mucilage layers that make it much more difficult for zooplankton ingestion than in the case of single cells. Failkowsak and Pajdak-Stos (2002) have recently shown that cyanobacteria are able to modify their defense reaction according to grazing risk. Despite these defensive reactions by some phytoplankton, their biomass was shown to decrease significantly during winter periods due to winter grazing by zooplankton (Garnier and Mourelatos, 1991).…”