Size Selective Feeding in Cyclidium glaucoma (Ciliophora, Scuticociliatida) and Its Effects on Bacterial Community Structure: A Study from a Continuous Cultivation System

Abstract

A B S T R A C TThree aspects of size selective feeding by the scuticociliate Cyclidium glaucoma were studied in continuous cultivation systems. Firstly, grazing-induced changes in abundance, biomass, and size structure of a bacterial community were investigated. Secondly, we studied possible grazingprotection mechanisms of bacteria as a response to permanent presence of the predator. And finally, we were looking for potential feedback mechanisms within this predator-prey relationship, i.e., how the ciliate population reacted to a changed, more grazing-protected bacterial community. The first stage of the cultivation system consisted of the alga Cryptomonas sp. and the accompanying mixed bacterial community. These organisms were transferred to two second stage vessels, a control stage without ciliates and a second one inoculated with C. glaucoma. After the first week, the abundance of bacteria in the latter decreased by 60% and remained stable until the end of the experiment (65 d), whereas bacterial biomass was less affected (393 µg C L −1 during days 0-7, 281 µg C L −1 afterwards). The mean bacterial cell volume doubled from 0.089 µm 3 to 0.167 µm 3 , which was mainly due to increasing cell widths. During the whole investigation period formation of colonies or filaments was not observed, but we found a clear feedback of ciliates on bacterial size. An increase in bacterial cell volume was always followed by a decline of the predator population, resulting in a yet undescribed type of microbial predator-prey relation. Literature and our own data on the optimal food size range grazed by C. glaucoma showed that bacterial cell width rather than length was responsible for that observed phenomenon. Finally, we suggest that uptake rates of spherical latex beads give only limited information on truly ingestible prey volumes and that prey geometry should be considered in future studies on size selective feeding of protists.

Spatio-temporal patterns of bacterioplankton production and community composition related to phytoplankton composition and protistan bacterivory in a dam reservoir

“…This partly contrasted with the conclusions drawn from previous short-term incubation studies, in which protistan grazing induced remarkable compositional shifts in bacterioplankton (see e.g. 2imek et al 2001, Horň ák et al 2006). This inconsistency is likely related to the different sampling strategy applied in the present study (3 wk intervals), which does not reflect the typical doubling times of 1 to 2 d detected for the reservoir bacteria (Horň ák et al 2006(Horň ák et al , 2imek et al 2006).…”

“…Cryptomonas sp., growing in a phosphorus-limited inorganic medium, served as a sole source of organic carbon for growth of accompanying bacteria with a doubling time of 1 to 2 d (e.g. 2imek et al , Posch et al 2001. Since the latter growth rates are quite comparable to those measured for bacterioplankton growing in situ on natural substrates present in the reservoir water (2imek et al 2006), the exudates of cryptophytes likely represent a rich substrate pool for bacteria.…”

“…Cell sizing was conducted using the semiautomatic image analysis systems LUCIA D (Lucia 3.52, Laboratory Imaging, Prague). Both approaches are detailed in Posch et al (1997) and2imek et al (2001).…”

“…Cell sizing was conducted using the semiautomatic image analysis systems LUCIA D (Lucia 3.52, Laboratory Imaging, Prague). Both approaches are detailed in Posch et al (1997) and2imek et al (2001).Bacterial production and carbon demand. BP was measured as incorporation of [ 3 H]-thymidine (ICN) using the method modified from Riemann & Sønder-gaard (1986); for details, see Stra$krabová et al (1999).…”

Effects of phosphorus loading on interactions of algae and bacteria: reinvestigation of the ‘phytoplankton-bacteria paradox’ in a continuous cultivation system

“…Bacterial and algal cells were counted after DAPI staining with a Zeiss Axioplan or a Zeiss Axiophot 2 (for algal counts) epifluorescence microscope following the protocol of Porter & Feig (1980). For a more detailed description of the methods see 2imek et al (1997) and Posch et al (2001). Mean cell volumes of organisms were determined by image-analysis (Lucia D, Laboratory Imaging: see www.lim.cz).…”