Changes in Bacterial and Eukaryotic Community Structure after Mass Lysis of Filamentous Cyanobacteria Associated with Viruses

Abstract

During an experiment in two laboratory-scale enclosures filled with lake water (130 liters each) we noticed the almost-complete lysis of the cyanobacterial population. Based on electron microscopic observations of viral particles inside cyanobacterial filaments and counts of virus-like particles, we concluded that a viral lysis of the filamentous cyanobacteria had taken place. Denaturing gradient gel electrophoresis (DGGE) of 16S ribosomal DNA fragments qualitatively monitored the removal of the cyanobacterial species from the community and the appearance of newly emerging bacterial species. The majority of these bacteria were related to the Cytophagales and actinomycetes, bacterial divisions known to contain species capable of degrading complex organic molecules. A few days after the cyanobacteria started to lyse, a rotifer species became dominant in the DGGE profile of the eukaryotic community. Since rotifers play an important role in the carbon transfer between the microbial loop and higher trophic levels, these observations confirm the role of viruses in channeling carbon through food webs. Multidimensional scaling analysis of the DGGE profiles showed large changes in the structures of both the bacterial and eukaryotic communities at the time of lysis. These changes were remarkably similar in the two enclosures, indicating that such community structure changes are not random but occur according to a fixed pattern. Our findings strongly support the idea that viruses can structure microbial communities.

Metagenomic approach studying the taxonomic and functional diversity of the bacterial community in a mesotrophic lake (Lac du Bourget – France)

“…Our metagenomic analysis suggests also that Bacteroidetes were associated with the metabolism of cell wall component of both bacteria and microalgae. This finding seems to be in agreement with several reports evidencing a strong relationship between the high abundance of Bacteroidetes and the elimination of cyanobacterial blooms (van Hannen et al, 1999;Rashidan and Bird, 2001).…”

Climate change: a catalyst for global expansion of harmful cyanobacterial blooms

“…For example, it has recently been shown that competition among toxic versus nontoxic strains is a major determinant of the overall toxicity of Microcystis blooms, and is strongly affected by the length of the spring-summer period and light availability (Kardinaal et al, 2007b). • Studies of viral infections, which may lead to mass lysis of cyanobacteria within a few days (Van Hannen et al, 1999;Hewson et al, 2001;Tucker and Pollard, 2005). This begs the question of whether the viralcyanobacterial interactions depend on temperature, and perhaps could respond strongly to climate change.…”

Intra‐ and inter‐lake variability of free‐living and particle‐associated Actinobacteria communities

“…Seasonal changes within aquatic bacterial communities are caused by numerous environmental factors, such as phytoplankton succession, protozoan grazing or viral lysis (Hahn and Höfle, 1999;Van Hannen et al, 1999;Brussaard et al, 2005;Newton et al, 2006). For Actinobacteria it has been proposed that phytoplankton-derived DOM (Stepanauskas et al, 2003), pH (Lindström et al, 2005) or grazing (Pernthaler et al, 2001;Jezbera et al, 2005;Newton et al, 2006) are determining factors for community structure.…”