Restructuring of Epibacterial Communities on Fucus vesiculosus forma mytili in Response to Elevated pCO2 and Increased Temperature Levels.

Birte Mensch,Sven C Neulinger,Sven Künzel,Andreas Pansch,Ruth A Schmitz,Angelika Graiff,Martin A Fischer

doi:10.3389/fmicb.2016.00434

Abstract

Marine multicellular organisms in composition with their associated microbiota—representing metaorganisms—are confronted with constantly changing environmental conditions. In 2110, the seawater temperature is predicted to be increased by ~5°C, and the atmospheric carbon dioxide partial pressure (pCO2) is expected to reach approximately 1000 ppm. In order to assess the response of marine metaorganisms to global changes, e.g., by effects on host-microbe interactions, we evaluated the response of epibacterial communities associated with Fucus vesiculosus forma mytili (F. mytili) to future climate conditions. During an 11-week lasting mesocosm experiment on the island of Sylt (Germany) in spring 2014, North Sea F. mytili individuals were exposed to elevated pCO2 (1000 ppm) and increased temperature levels (Δ+5°C). Both abiotic factors were tested for single and combined effects on the epibacterial community composition over time, with three replicates per treatment. The respective community structures of bacterial consortia associated to the surface of F. mytili were analyzed by Illumina MiSeq 16S rDNA amplicon sequencing after 0, 4, 8, and 11 weeks of treatment (in total 96 samples). The results demonstrated that the epibacterial community structure was strongly affected by temperature, but only weakly by elevated pCO2. No interaction effect of both factors was observed in the combined treatment. We identified several indicator operational taxonomic units (iOTUs) that were strongly influenced by the respective experimental factors. An OTU association network analysis revealed that relationships between OTUs were mainly governed by habitat. Overall, this study contributes to a better understanding of how epibacterial communities associated with F. mytili may adapt to future changes in seawater acidity and temperature, ultimately with potential consequences for host-microbe interactions.

Highlights

The surfaces of marine macroalgae offer a diverse substrate for attachment and are often colonized by a large variety of bacteria acquired from nearby macroalgae and from the surrounding waters (Lachnit et al, 2011; Egan et al, 2013; Stratil et al, 2013, 2014)
A distance biplot visualizing the general type effect throughout the experiment is shown in Figure 1, with samples of F. mytili biofilm and water forming separated clusters
In every week and treatment, the biofilm attached to the F. mytili surface was generally dominated by Proteobacteria, Bacteroidetes (Flavobacteria, Saprospirae, Cytophagia, BME43 cluster), and Actinobacteria (Acidimicrobiia; Figure 2)

Summary

Introduction

The surfaces of marine macroalgae offer a diverse substrate for attachment and are often colonized by a large variety of bacteria acquired from nearby macroalgae and from the surrounding waters (Lachnit et al, 2011; Egan et al, 2013; Stratil et al, 2013, 2014). Macroalgal host and microbiota mutually benefit from each other by e.g., nutrient exchange (Hellio et al, 2000; Goecke et al, 2010; Lachnit et al, 2010; Nasrolahi et al, 2012), and microbial biofilms attached to the surface offer a protective layer against e.g., settlement of larvae (Nasrolahi et al, 2012; Egan et al, 2013). Several other factors shaping microbial communities might be affected by environmental changes and need to be considered: e.g., the complex bacteria-bacteria interactions (cooperation and competition) within epibacterial communities, predatory bacteria like Bdellovibrio and like organisms (BALOs), or organic matter provided by the algal (recently reviewed by Dang and Lovell, 2016)

Methods

Results

Conclusion