Bacterial communities associated with Microcystis colonies differ from free‐living communities living in the same ecosystem

Abstract

The search for a better understanding of why cyanobacteria often dominate phytoplankton communities in eutrophic freshwater ecosystems has led to a growing interest in the interactions between cyanobacteria and bacteria. Against this background, we studied the location of bacteria within Microcystis colonies, and compared the structural and phylogenetic diversity of Microcystis-attached and free-living bacterial communities living in the same French lake, the Villerest reservoir. Using transmission electron microscopy, we show that most of the bacteria inside the colonies were located close to detrital materials that probably resulted from lysis of Microcystis cells. The 16S rRNA sequencing approach revealed a clear distinction between the attached and free-living communities at the levels of both their general structure and their operational taxonomic unit (OTU) composition. In particular, Microcystis colonies appeared to be depleted of Actinobacteria, but conversely enriched in Gammaproteobacteria, in particular when the bloom was declining. At the OTU level, a clear distinction was also found between attached and free-living bacteria, and new clades were identified among our sequences. All these findings suggest that Microcystis colonies constitute a distinct habitat for bacteria living in freshwater ecosystems, and that direct and indirect interactions (cell lysis, nutrient recycling, etc.) may occur between them inside these colonies.

Characterising and predicting cyanobacterial blooms in an 8-year amplicon sequencing time course

“…The order Chthoniobacterales (in the phylum Verrucomicrobia) was also found as a bloom biomarker, consistent with previous studies that observed this taxon in association with Anabaena blooms (Louati et al, 2015). Other studies have reported specific association between Verrucomicrobia and Cyanobacteria, suggesting that members of this phylum might assimilate cyanobacterial metabolites (Parveen et al, 2013;Louati et al, 2015). We also found N 2 -fixing members of Rhizobiales order as bloom biomarkers.…”

Bacterial Community Composition of Size-Fractioned Aggregates within the Phycosphere of Cyanobacterial Blooms in a Eutrophic Freshwater Lake

“…Thus, all these communities were highly specialized, and as there were major differences among communities, we conclude that they were affected by the phycosphere conditions created by cyanobacteria. Others have also observed the selection of specific bacterial species within the Microcystis phycosphere by comparing Microcycstis -attached bacteria (phycosphere bacteria) with other microbial communities living in the same aquatic ecosystem [11], [13].…”

Variation of bacterial communities in water and sediments during the decomposition of Microcystis biomass

“…Cyanobacterial blooms, especially Microcystis blooms, are frequently found in eutrophic freshwater ecosystems and can pose notable risks to ecological and human health [3–5]. Bacterial communities associated with marine phytoplankton blooms [2, 6–7] and bloom-forming freshwater phytoplankton in growing stage [1, 8] have also received considerable attention. In contrast, only a few studies have examined the bacterial community composition in response to the breakdown of algal blooms in freshwater lakes [9–11].…”