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Phytoplankton needs allies

​As part of an international collaboration, researchers from LI2D (SPI / Marcoule) and University of Warwick have highlighted the long-term benefits of the association between different marine microorganisms. The study published in Nature Microbiology shows that, contrary to what was admitted up to now, these microorganisms are in equilibrium and not in competition for micronutrients, because they form a complementary ecosystem. In a form of ocean-scale symbiosis, some of them "detoxify" the environment of others.

Published on 30 June 2017


Biological interactions underpin the functioning of marine ecosystems, be it via competition, predation, mutualism or symbiosis processes. Microbial phototroph–heterotroph interactions propel the engine that results in the biogeochemical cycling of individual elements, and they are critical for understanding and modelling global ocean processes. Unfortunately, studies thus far have focused on exponentially growing cultures in nutrient-rich media, meaning knowledge of such interactions under in situ conditions is rudimentary at best. Here, we have performed long-term phototroph–heterotroph co-culture experiments under nutrient-amended and natural seawater conditions, and show that it is not the concentration of nutrients but rather their circulation that maintains a stable interaction and a dynamic system. Using the SynechococcusRoseobacter interaction as a model phototroph–heterotroph case study, we show that although Synechococcus is highly specialized for carrying out photosynthesis and carbon fixation, it relies on the heterotroph to remineralize the inevitably leaked organic matter, making nutrients circulate in a mutualistic system. In this sense we challenge the general belief that marine phototrophs and heterotrophs compete for the same scarce nutrients and niche space, and instead suggest that these organisms more probably benefit from each other because of their different levels of specialization and complementarity within long-term stable-state systems.

Read the French version.

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