Host–microbe interactions as a driver of acclimation to salinity gradients in brown algal cultures

Abstract

Like most eukaryotes, brown algae live in association with bacterial communities that frequently have beneficial effects on their development. Ectocarpus is a genus of small filamentous brown algae, which comprises a strain that has recently colonized freshwater, a rare transition in this lineage. We generated an inventory of bacteria in Ectocarpus cultures and examined the effect they have on acclimation to an environmental change, that is, the transition from seawater to freshwater medium. Our results demonstrate that Ectocarpus depends on bacteria for this transition: cultures that have been deprived of their associated microbiome do not survive a transfer to freshwater, but restoring their microflora also restores the capacity to acclimate to this change. Furthermore, the transition between the two culture media strongly affects the bacterial community composition. Examining a range of other closely related algal strains, we observed that the presence of two bacterial operational taxonomic units correlated significantly with an increase in low salinity tolerance of the algal culture. Despite differences in the community composition, no indications were found for functional differences in the bacterial metagenomes predicted to be associated with algae in the salinities tested, suggesting functional redundancy in the associated bacterial community. Our study provides an example of how microbial communities may impact the acclimation and physiological response of algae to different environments, and thus possibly act as facilitators of speciation. It paves the way for functional examinations of the underlying host-microbe interactions, both in controlled laboratory and natural conditions.

Climate Change Impacts on Seagrass Meadows and Macroalgal Forests: An Integrative Perspective on Acclimation and Adaptation Potential

“…Increased physical disturbances and stress, resulting from changing environmental conditions, are known to affect the macroalgae-associated microbial composition (directly or via its physiological responses) and cause its structural, functional or behavioral changes (Goecke et al, 2010;Egan et al, 2013;Hollants et al, 2013;Dittami et al, 2016). Microorganisms seem to be able to play a pivoting role in enabling macrophytes to expand their physiological capacities, broadening their environmental tolerance (Goecke et al, 2010;Egan et al, 2013;Hollants et al, 2013).…”

“…Microorganisms seem to be able to play a pivoting role in enabling macrophytes to expand their physiological capacities, broadening their environmental tolerance (Goecke et al, 2010;Egan et al, 2013;Hollants et al, 2013). In a species of the genus Ectocarpus for example, specific bacteria are linked to low salinity tolerance in Ectocarpus cultures facilitating acclimation to environmental change (Dittami et al, 2016). To what extend the marine macrophyte microbiome could be involved in thermal acclimation and adaptation is not known.…”

“…At this moment, few studies address this issue in seagrasses and macroalgae. However some evidences are already documented in filamentous algae (Dittami et al, 2016). Holobiont evolution requires strict partner fidelity and will only work under vertical transmission fidelity and can be evolutionary unstable due to microbial cheaters, or shifting cost:benefit ratios (Douglas and Werren, 2016).…”

Biotic interactions as drivers of algal origin and evolution

“…These findings suggest the existence of chemical signaling between bacteria and the alga, and, potentially, the complementarity of metabolic pathways. Similar interactions have also been found between the bacterium Sulfitobacter pseudonitzschiae and the diatom Pseudo‐nitzschia multiseries (Amin et al ., ), and bacteria have been shown to facilitate the acclimation of the brown seaweed Ectocarpus siliculosus to a freshwater environment (Dittami et al ., ). Another striking example of this phenomenon is the ‘Jekyll‐and‐Hyde’ (named by the authors) relationship between Phaeobacter gallaeciensis , a biofilm‐forming roseobacter, and the bloom‐forming haptophyte alga Emiliania huxleyi (Seyedsayamdost et al ., ).…”

Microbial communities mediating algal detritus turnover under anaerobic conditions

“…The size, intensity, and duration of these bloom-mediated anoxic zones are expected to be accentuated by future global warming trends (Paerl & Otten, 2013). Surprisingly, while a large body of research has been conducted on elucidating the microbial community composition of the algal phycosphere in the aerobic surficial marine (Amin, Parker & Armbrust, 2012; Hasegawa et al, 2007; Sapp, Wichels & Gerdts, 2007), and freshwater habitats (Bagatini et al, 2014; Cai et al, 2014; Dittami et al, 2016; Eigemann et al, 2013; Jones et al, 2013; Muylaert et al, 2002), a surprising lack of knowledge exists regarding the microbial community and patterns of algal turnover under the anoxic conditions in the lower layers of stratified water bodies.…”