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.
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Acknowledgements
We are grateful to Catherine Leblanc, Christian Jeanthon, Dominique Davoult, Philippe Potin, Elianne Sirnæs Egge and Tristan Barbeyron for helpful advice on the experimental setup and analysis. We also thank Ludovic Delage for providing Zobellia galactanivorans DNA, Akira Peters (BEZHIN ROSKO) for providing algal strains, Declan Schroeder for allowing us to use the two South African algal strains, Laurence Dartevelle for performing antibiotic treatments on strain 371, Jonas Collén for critical reading of the manuscript, and the Biogenouest Genomics and Genomer platform core facility for technical support. This work benefited from the support of the French Government via the National Research Agency investment expenditure program IDEALG (ANR-10-BTBR-02-04) and additional support came from the region Brittany via the SAD (Stratégie d’Attractivité Durable) project COGEBRAL.
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Dittami, S., Duboscq-Bidot, L., Perennou, M. et al. Host–microbe interactions as a driver of acclimation to salinity gradients in brown algal cultures. ISME J 10, 51–63 (2016). https://doi.org/10.1038/ismej.2015.104
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DOI: https://doi.org/10.1038/ismej.2015.104
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