Seasonal succession and taxon-specific bacterial grazing rates of heterotrophic nanoflagellates in Lake Constance

Abstract

We investigated the taxonomic composition of the heterotrophic nanoflagellate (HNF) assemblage and its taxon-specific bacterial grazing rates in Lake Constance (Germany) over the course of 1 yr. Bacterial grazing rates were measured using natural fluorescently labelled bacteria (FLB) and compared to bacterial production estimated by the uptake of 14 C-leucine incorporation. Glutaraldehyde-fixed, DAPI-stained flagellates were counted using epifluorescence microscopy. Based on annual averages, small species such as Spumella sp. (2 to 6 µm) were the most numerous HNF and the dominant bacterivores. Larger flagellates such as Kathablepharis sp. contributed significantly to total HNF biomass, in particular during spring, but were relatively unimportant as bacterial grazers. The HNF community structure changed during the transition from the phytoplankton spring bloom to the clearwater phase, with small flagellates such as heterokonts, kinetoplastids and choanoflagellates becoming increasingly abundant. The flagellate community composition was more diverse during summer and autumn than in spring. Per capita ingestion rates ranged from 0 to 31 bacteria HNF -1 h -1 and changed seasonally up to 10-fold within a given taxon. Mixotrophic species contributed little to total bacterivory. We provide evidence that the relative significance of bacterial ingestion by a given flagellate taxon may change seasonally. Based upon our experimental results, we discuss potential shortcomings inherent in the FLB technique.KEY WORDS: Heterotrophic nanoflagellates (HNF) · Seasonal succession · FLB · Grazing rate · Negative binomial distribution · Lake ConstanceResale or republication not permitted without written consent of the publisher

Diversity and vertical distribution of planktonic ciliates in a stratified mesotrophic lake: relationship to environmental conditions

“…Many authors (e.g. Porter et al 1988, Carrias et al 1998, Cleven & Weisse 2001 have shown positive correlations between the total numbers of planktonic ciliates and the abundance of heterotrophic nanoflagellates. Šimek et al (1998) reported that flagellates control bacterial populations and are themselves food for many ciliates.…”

“…Ciliates play a significant role in energy transfer and nutrient remineralization in aquatic environments (Cleven & Weisse 2001). They are grazers of autotrophic and heterotrophic pico-and nanoplankton, and prey for micrometazoans.…”

Vertical micro-distribution of psammonic ciliates and their relationship to physical and chemical parameters in two lakes of different trophic status

“…These microorganisms are important consumers of bacteria, flagellates, and algae; they also participate in the decomposition of organic matter and nutrient cycling. Ciliates have been quite widely used as indicators of water pollution (Fenchel 1987;Finlay, Esteban 1998;Cleven, Weisse 2001;Mieczan 2008). However, the vertical micro-distribution of ciliates has not been studied with respect to lake trophy.…”

Multigene phylogenies of clonal Spumella-like strains, a cryptic heterotrophic nanoflagellate, isolated from different geographical regions

“…(Auer & Arndt, 2001;Cleven & Weisse, 2001;Weitere & Arndt, 2003). These organisms account for a substantial proportion of the heterotrophic nanoflagellate (HNF) biomass, especially in freshwater systems (Domaizon et al, 2003;Felip et al, 1999;Zhao et al, 2003), and play a major role in microbial ecology as Abbreviations: ED, evolutionary distance; ITS, internal transcribed spacer; ML, maximum likelihood; PP, posterior probability; SSU, small subunit.…”

“…However, merging different taxa into 'black boxes' is insufficient to describe specific interactions and pathways within microbial food webs. Therefore, an increasing effort to focus on species-or taxonspecific investigations has arisen (Cleven & Weisse, 2001). …”