Exploring the inhibition of targeted microalgae by a Cylindrotheca closterium nonaxenic biofilm
Résumé
Monospecific microalgal dominance in nutrient-rich environments is usually attributed to exclusive resource competition or grazing selectivity. However, allelopathic interactions within microalgal communities may reinforce established dominance and limit species replacement. While many allelopathic interaction studies among autotrophic microorganisms focused on aquatic free-living species, scarce knowledge exists on microalgae aquatic biofilms, although chemical communication between species or communities is favored due to spatial proximity. We thus developed and applied a co-culture protocol using a disc diffusion method to evidence the inhibitory potential of biofilms of the marine diatom Cylindrotheca closterium growing in non-axenic conditions on different targeted microalgal strains. The biofilm exhibited an inhibitory effect on the individual growth of two microalgal strains, Nannochloropsis oculata and Tetraselmis striata, but did not affect the microalga Porphyridium purpureum. Bacteria isolated from the inhibition zone did not show any inhibitory activity on targeted microalgae. This suggests that the growth inhibition and cell deformation observed for the two sensitive microalgal strains may result from compounds produced during the growth of C. closterium biofilm or from associated bacteria identified but not isolated in the present study. Therefore, further investigations are required to identify the compounds and their microbial producers involved in the observed inhibition.
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