Bacterial Communities Associated with Four Cyanobacterial Genera Display Structural and Functional Differences: Evidence from an Experimental Approach.

Lin Zhu,Anouk Zancarini,Cécile Bernard,Julie Leloup,Imen Louati,Silvia De Cesare,Charlotte Duval,Lirong Song,Jean-François Humbert,Kevin Tambosco,Didier Debroas

doi:10.3389/fmicb.2016.01662

Abstract

To overcome the limitations associated with studying the interactions between bacterial communities (BCs) and cyanobacteria in natural environments, we compared the structural and functional diversities of the BCs associated with 15 non-axenic cyanobacterial strains in culture and two natural BCs sampled during cyanobacterial blooms. No significant differences in richness and diversity were found between the natural and cultivated BCs, although some of the cyanobacterial strains had been isolated 11 years earlier. Moreover, these BCs shared some similar characteristics, such as a very low abundance of Actinobacteria, but they display significant differences at the operational taxonomic unit (OTU) level. Overall, our findings suggest that BCs associated with cyanobacteria in culture are good models to better understand the interactions between heterotrophic bacteria and cyanobacteria. Additionally, BCs associated with heterocystous cyanobacterial strains cultivated in Z8X culture medium without nitrate (Aphanizomenon–Dolichospermum) demonstrated significant differences compared to BCs associated with non-heterocystous strains cultivated in Z8 culture medium (Planktothrix–Microcystis) in terms of their composition and their ability to utilize different carbon sources, suggesting the potential influence of cyanobacterial metabolism and/or culture media on associated BCs. Finally, half of the dominant OTUs in these BCs were specifically associated with cyanobacteria or other phytoplankton, whereas the remaining OTUs were generally associated with ecosystems containing high organic matter content, such as sludge or intestines.

Highlights

MATERIALS AND METHODSIn the last 10 years, a growing number of published studies have investigated the bacterial communities (BCs) associated with phytoplankton
Comparison of the global composition and structure of the BCs associated with cyanobacteria in culture and those associated with natural blooms of Dolichospermum and Microcystis revealed a shared dominance by Proteobacteria, Alphaproteobacteria, and Bacteroidetes in these communities
These BCs primarily differed in terms of the relative abundances of Actinobacteria and Betaproteobacteria and, to a lesser extent, Verrucomicrobia (Figure 1); these phyla were more abundant in BCs associated with cyanobacteria in natural blooms than those in culture

Summary

Introduction

MATERIALS AND METHODSIn the last 10 years, a growing number of published studies have investigated the bacterial communities (BCs) associated with phytoplankton. The majority of studies have focused on cyanobacterial blooms due to their potential impact on human health (e.g., Dodds et al, 2009). Several publications have evaluated the impact of cyanobacterial blooms on the structure and composition of BCs within the same ecosystems (e.g., Eiler and Bertilsson, 2004; Berg et al, 2009; Louati et al, 2015; Woodhouse et al, 2016). Microcystis sp., a toxic bloom-forming cyanobacteria, has been a specific focus given its high prevalence in many ecosystems around the world as well as its colonial organization, which offers a potential niche and physical support for direct interactions with heterotrophic prokaryotes (e.g., Shen et al, 2011; Li et al, 2012; Shi et al, 2012; Shao et al, 2014)

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