AUTHOR=Vacant Sophie , Benites L. Felipe , Salmeron Christophe , Intertaglia Laurent , Norest Manon , Cadoudal Adrien , Sanchez Frederic , Caceres Carlos , Piganeau Gwenael 

TITLE=Long-Term Stability of Bacterial Associations in a Microcosm of Ostreococcus tauri (Chlorophyta, Mamiellophyceae)

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.814386

DOI=10.3389/fpls.2022.814386

ISSN=1664-462X

ABSTRACT=<p>Phytoplankton–bacteria interactions rule over carbon fixation in the sunlit ocean, yet only a handful of phytoplanktonic–bacteria interactions have been experimentally characterized. In this study, we investigated the effect of three bacterial strains isolated from a long-term microcosm experiment with one <italic>Ostreococcus</italic> strain (Chlorophyta, Mamiellophyceae). We provided evidence that two <italic>Roseovarius</italic> strains (Alphaproteobacteria) had a beneficial effect on the long-term survival of the microalgae whereas one <italic>Winogradskyella</italic> strain (Flavobacteriia) led to the collapse of the microalga culture. Co-cultivation of the beneficial and the antagonistic strains also led to the loss of the microalga cells. Metagenomic analysis of the microcosm is consistent with vitamin B12 synthesis by the <italic>Roseovarius</italic> strains and unveiled two additional species affiliated to <italic>Balneola</italic> (Balneolia) and <italic>Muricauda</italic> (Flavobacteriia), which represent less than 4% of the reads, whereas <italic>Roseovarius</italic> and <italic>Winogradskyella</italic> recruit 57 and 39% of the reads, respectively. These results suggest that the low-frequency bacterial species may antagonize the algicidal effect of <italic>Winogradskyella</italic> in the microbiome of <italic>Ostreococcus tauri</italic> and thus stabilize the microalga persistence in the microcosm. Altogether, these results open novel perspectives into long-term stability of phytoplankton cultures.</p>