Structural Diversity of Bacterial Communities Associated with Bloom-Forming Freshwater Cyanobacteria Differs According to the Cyanobacterial Genus

Imen Louati,Julie Leloup,Didier Debroas,Jean-François Humbert,Noémie Pascault,Cécile Bernard,Wolfgang R Hess

doi:10.1371/journal.pone.0140614

Abstract

The factors and processes driving cyanobacterial blooms in eutrophic freshwater ecosystems have been extensively studied in the past decade. A growing number of these studies concern the direct or indirect interactions between cyanobacteria and heterotrophic bacteria. The presence of bacteria that are directly attached or immediately adjacent to cyanobacterial cells suggests that intense nutrient exchanges occur between these microorganisms. In order to determine if there is a specific association between cyanobacteria and bacteria, we compared the bacterial community composition during two cyanobacteria blooms of Anabaena (filamentous and N2-fixing) and Microcystis (colonial and non-N2 fixing) that occurred successively within the same lake. Using high-throughput sequencing, we revealed a clear distinction between associated and free-living communities and between cyanobacterial genera. The interactions between cyanobacteria and bacteria appeared to be based on dissolved organic matter degradation and on N recycling, both for N2-fixing and non N2-fixing cyanobacteria. Thus, the genus and potentially the species of cyanobacteria and its metabolic capacities appeared to select for the bacterial community in the phycosphere.

Highlights

The global incidence and severity of cyanobacterial blooms have expanded during the past decades due to the eutrophication of many freshwater ecosystems and to climate warming [1]
Despite the increasing body of literature available on this phenomenon, it remains difficult to predict the onset, duration and intensity of blooms in a given ecosystem. This is in part due to a lack of knowledge concerning the processes leading to the dominance of cyanobacteria among the microbial primary producers and on the interactions between phototrophic and chemotrophic microorganisms [2]
We found some Uncultured cyanobacteria during both blooms

Summary

Introduction

The global incidence and severity of cyanobacterial blooms have expanded during the past decades due to the eutrophication of many freshwater ecosystems and to climate warming [1]. Despite the increasing body of literature available on this phenomenon, it remains difficult to predict the onset, duration and intensity of blooms in a given ecosystem. This is in part due to a lack of knowledge concerning the processes leading to the dominance of cyanobacteria among the microbial primary producers and on the interactions between phototrophic and chemotrophic microorganisms [2]. Bacterial Diversity Associated to Cyanobacteria outcompete other phytoplanktonic microorganisms due to their high adaptive capacities for nutrient and light harvesting and their cellular organization in colonies or filaments [3]. The lower growth during the exponential phase of axenic Microcystis aeruginasa cultures as compared to nonaxenic cultures [4] and the increase in nitrogen fixing (N2) capacities and growth in Anabaena spp. after addition of bacteria in cultures after addition of bacteria in cultures [5] suggests that these interactions might be important for cyanobacterial fitness

Methods

Results

Conclusion