Abstract
The thallus surface of the brown macroalga Fucus vesiculosus is covered by a specific biofilm community. This biofilm supposedly plays an important role in the interaction between host and environment. So far, we know little about compositional or functional shifts of this epibiotic bacterial community under changing environmental conditions. In this study, the response of the microbiota to different temperatures with respect to cell density and community composition was analyzed by nonculture-based methods (denaturing gradient gel electrophoresis and 454 pyrosequencing of the 16S rRNA gene). Redundancy analysis showed that despite high variability among host individuals temperature accounted for 20% of the variation in the bacterial community composition, whereas cell density did not differ between groups. Across all samples, 4341 bacterial operational taxonomic units (OTUs) at a 97% similarity level were identified. Eight percent of OTUs were significantly correlated with low, medium, and high temperatures. Notably, the family Rhodobacteraceae increased in relative abundance from 20% to 50% with increasing temperature. OTU diversity (evenness and richness) was higher at 15°C than at the lower and higher temperatures. Considering their known and presumed ecological functions for the host, change in the epibacterial community may entail shifts in the performance of the host alga.
Highlights
The important roles of surface-associated biofilms in transepidermal exchange processes and other interactions between host and environment have recently been described (Wahl et al 2012)
We investigated the effect of temperature (5, 10, 15, 20, and 25°C) on the bacterial community composition (n = 5 per temperature level) after 14 days of incubation and on cell density (n = 3 per temperature level, except for n = 2 at 5°C) after 28 days of incubation
In order to assess the effect of temperature on the bacterial community composition associated with the thallus surface of the brown macroalga, F. vesiculosus, we chose the fingerprinting method Denaturing Gradient Gel Electrophoresis” (DGGE) as a way to give a first overview of potential community shifts
Summary
The important roles of surface-associated biofilms in transepidermal exchange processes and other interactions between host and environment have recently been described (Wahl et al 2012). Studies of the “microbiome,” that is, entire microbial communities in environmental samples, have become possible with the aid of high-throughput sequencing methods (Margulies et al 2005) These studies have highlighted the diversity, specificity, and dynamics of these communities, for example, in air (Bowers et al 2011), in water (Gilbert et al 2012), in soil (Roesch et al 2007), in sands (Gobet et al 2012), and associated with hosts. Temperature deserves attention in experiments because at the sea surface it is predicted to increase in the Western Baltic by 0.5–2.5°C (Neumann and Friedland 2011) or even 4°C (BACC Author Team 2008) within the century, respectively, depending on the model This will possibly cause stress for the alga species and may restructure its epibacterial community. We predicted that temperature will lead to shifts in the bacterial community composition and would increase the overall number of bacterial cells on the thallus
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