Quantitative dominance of seasonally persistent filamentous cyanobacteria (Planktothrix rubescens) in the microbial assemblages of a temperate lake

Abstract

The spatiotemporal changes in abundance and biomass of heterotrophic bacteria, of three major bacterial phylogenetic groups, and of picocyanobacteria in the upper 20 m of a deep prealpine lake (Lake Zurich, Switzerland) were monitored during a seasonally persistent bloom of the toxigenic filamentous cyanobacterium Planktothrix rubescens. In addition, bacterial 16S ribosomal deoxyribonucleic acid (rDNA) sequences were collected at one instance from the bloom layer and from waters above and below this zone. P. rubescens comprised up to 70% of particulate organic carbon during summer stratification and autumnal mixis and thus by far exceeded the total biomass both of other phytoplankton and of prokaryotes. A strong negative correlation was found between the estimated basin-wide biomass of P. rubescens and of heterotrophic bacteria, and there was different spatial niche preference of filamentous vs. picocyanobacteria. Only members of the CytophagaFlavobacterium lineage of Bacteroidetes showed an increasing tendency of association with the P. rubescens population, in particular at the onset of autumnal mixing. Although the filamentous cyanobacterium was the dominant primary producer throughout the year, it did not seem to be a carbon source for heterotrophic bacteria at all. We conclude that P. rubescens represents a powerful competitor of autotrophic and heterotrophic prokaryotes, likely due to both its specific physiological (photoheterotrophic) properties and its protection against zooplankton grazing. This competitiveness might be regarded as another reason for its mass occurrence in numerous lakes of the Northern hemisphere.

Short‐term displacement of Planktothrix rubescens (cyanobacteria) in a pre‐alpine lake observed using an autonomous sampling platform

“…The autofluorescent filaments under green light were quantified by automated image analysis (Zeder et al 2010). Counts were translated into biovolumes (Van den Wyngaert et al 2011).…”

Vertical and longitudinal distribution patterns of different bacterioplankton populations in a canyon‐shaped, deep prealpine lake

“…Phylogenetic analyses and probe design of 16S ribosomal ribonucleic acid (rRNA) genes was done with sequences obtained during autumn 2007 (water samples from 10-, 12.5-, and 15-m depth; Van Den Wyngaert et al 2011;Salcher et al 2011). Four hundred forty-six sequences of Lake Zurich were deposited to the European Molecular Biology Laboratory with the accession no.…”

“…Vertical gradients in temperature and light shape the microbial assemblages in the sea (Johnson et al 2006;Zwirglmaier et al 2008) and, even more pronounced, in lakes (Salcher et al 2010;Van Den Wyngaert et al 2011). Phototrophic microbes such as picocyanobacteria (Johnson et al 2006;Zwirglmaier et al 2008;Van Den Wyngaert et al 2011), and aerobic anoxygenic phototrophs (Salka et al 2008), or rhodopsin-bearing heterotrophic bacteria (Giovannoni et al 2005;Sharma et al 2009) are usually only abundant in the photic zone of oceans and lakes.…”

“…Phototrophic microbes such as picocyanobacteria (Johnson et al 2006;Zwirglmaier et al 2008;Van Den Wyngaert et al 2011), and aerobic anoxygenic phototrophs (Salka et al 2008), or rhodopsin-bearing heterotrophic bacteria (Giovannoni et al 2005;Sharma et al 2009) are usually only abundant in the photic zone of oceans and lakes. Moreover, many eukaryotic algae in the well-illuminated surface-water layers are accompanied by a distinct bacterial community thriving on phytoplankton exudates (Grossart et al 2005).…”

“…This filamentous cyanobacterium (mean size , 500 mm) contains several toxic secondary metabolites (e.g., hepatotoxic microcystins) as an effective protection against grazing by zooplankton, and these metabolites are also considered as harmful for humans (Blom et al 2006). P. rubescens is adapted to low light irradiances and usually forms dense layers in 10-15-m depth (i.e., in the metalimnion) in late summer to autumn (Van Den Wyngaert et al 2011). It is not yet clear whether the persistent layer of P. rubescens is a lake-basin-wide phenomenon or whether it forms local blooms.…”